Lake Vostok is potentially important to scientists because it________.

The mineral particles found in soil range in size from microscopic clay particles to large boulders. The most abundant particles - sand, silt, and clay - are the focus of examination in studies of soil texture. Texture is the term used to describe the line composite sizes of particles in a soil sample, typically several representative handfuls . To measure soil texture, the sand, silt, and clay particles are sorted out by size and weight. The weights of each size are then expressed as a percentage of the sample weight. In the field, soil texture can be estimated by extracting a handful of sod and squeezing the damp soil into three basic shapes; (1) cast, a lump formed by squeezing a sample in a clenched fist; (2) thread, a pencil shape formed by rolling soil between the palms; and (3) ribbon, a flatfish shape formed by squeezing a small sample between the thumb and index finger. The behavioral characteristics of the soil when molded into each of these shapes, if they can be formed at all, provides the basis for a general textural classification. The behavior of the soil in the hand test is determined by the amount of clay in the sample. Clay particles are highly cohesive, and when dampened , behave as a plastic. Therefore the higher the clay content in a sample, the more refined and durable the shapes into which it can be molded. Another method of determining soil texture involves the use of devices called sediment sieves, screens built with a specified mesh size. When the soil is filtered through a group of sieves, each with a different mesh size, the particles become grouped in corresponding size categories. Each category can be weighed to make a textural determination. Although sieves work well for silt, sand, and larger particles, they are not appropriate for clay particles. Clay is far too small to sieve accurately; therefore, in soils with a high proportion of clay, the fine particles are measured on the basis of their settling velocity when suspended in water. Since clays settle so slowly, they are easily segregated from sand and silt. The water can be drawn off and evaporated, leaving a residue of clay, which can be weighed.

During the procedure described in paragraph 3, when clay particles are placed into water they ______.

The word "related" in paragraph 1 is closest in meaning to _______.

Thanksgiving is celebrated in the US on the fourth Thursday in November. For many Americans it is the most important holiday apart from Christmas. Schools, offices and most businesses close for Thanksgiving, and many people make the whole weekend a vacation. Thanksgiving is associated with the time when Europeans first came to North America. In 1620 the ship the Mayflowers arrived, bringing about 150 people who today are usually called Pilgrims. They arrived at the beginning of a very hard winter and could not find enough to eat, so many of them died. But in the following summer Native Americans showed them what foods were safe to eat, so that they could save food for the next winter. They held a big celebration to thank God and the Native Americans for the fact that they had survived. Today people celebrate Thanksgiving to remember these early days. The most important part of the celebration is a traditional dinner with foods that come from North America. The meal includes turkey, sweet potatoes (also called yams) and cranberries, which are made into a kind of sauce or jelly. The turkey is filled with stuffing or dressing, and many families have their own special recipe. Dessert is pumpkin made into a pie. On Thanksgiving there are special television programs and sports events. In New York there is the Macy's Thanksgiving Day Parade, when a long line of people wearing fancy costumes march through the streets with large balloons in the shape of imaginary characters. Thanksgiving is considered the beginning of the Christmas period, and the next day many people go out to shop for Christmas presents. 

What is the purpose of the passage?

“Bricks” are mentioned in paragraph 3 to indicate how _______.

The word "fine" in the passage is closest in meaning to ______.

In Science, a theory is a reasonable explanation of observed events that are related. A theory often involves an imaginary model that helps scientists picture the way an observed event could be produced. A good example of this is found in the kinetic molecular theory, in which gases are pictured as being made up of many small particles that are in constant motion. After a theory has been publicized, scientists design experiments to test the theory. If observations confirm the scientists’ predictions, the theory is supported. If observations do not confirm the predictions, the scientists must search further. There may be a fault in the experiment, or the theory may have to be revised or rejected. Science involves imagination and creative thinking as well as collecting information and performing experiments. Facts by themselves arc not science. As the mathematician Jules Henri Poincare said: "Science is built with facts just as a house is built with bricks, but a collection of facts cannot be called science any more than a pile of bricks can be called a house." Most scientists start an investigation by finding out what other scientists have learned about a particular problem. After known facts have been gathered, the scientist comes to the part of the investigation that requires considerable imagination. Possible solutions to the problem are formulated. These possible solutions are called hypotheses. In a way, any hypothesis is a leap into the unknown. It extends the scientist's thinking beyond the known facts. The scientist plans experiments, performs calculations, and makes observations to test hypotheses. For without hypotheses, further investigation lacks purpose and direction. When hypotheses are confirmed, they are incorporated into theories. 

Which of the following is the main subject of the passage?

In developing countries, where three fourths of the world's population live, sixty percent of the people who can’t read and write are women. Being illiterate doesn’t mean they are not intelligent. It does mean it is difficult for them to change their lives. They produce more than half of the food. In Africa eighty percent of all agricultural work is done by women. There are many programs to help poor countries develop their agriculture. However, for years, these programs provided money and training for men. In parts of Africa, this is a typical day for a village woman. At 4:45 a.m, she gets up, washes and eats. It takes her a half hour to walk to the fields, and she works there until 3:00 p.m. She collects firewood and gets home at 4:00. She spends the next hour and a half preparing food to cook. Then she collects water for another hour. From 6:30 to 8:30 she cooks. After dinner, she spends an hour washing the dishes and her children. She goes to bed at 9:30 p.m. International organizations and programs run by developed nations are starting to help women, as well as men, improve their agricultural production. Governments have already passed some laws affecting women because of the UN Decade for Women. The UN report will affect the changes now happening in the family and society. 

What does the word "run" in the last paragraph mean?