Polluting the air, soil, and water can harm ecosystems. Building (3)_______ on rivers for electric power and irrigation can harm ecosystems around the rivers.

There can be no doubt at all that the Internet has made a huge difference to our lives. Parents are worried that children spend too much time playing on the Internet, hardly (1)_____ doing anything else in their spare time. Naturally, parents are (2)_____ to find out why the internet is so attractive, and they want to know if it can be harmful for their children. Should parents worry if their children are spending that much time (3)_____ their computer? Obviously, if children are bent over their computer for hours, (4)_____ in some game, instead of doing their homework, then something is wrong. Parents and children could decide how much use the children should make of the Internet, and the child should give his or her (5)____ that it won't interfere with homework. If the child is not holding to this arrangement, parents can take more drastic steps. Dealing with a child's use of the internet is not much different from negotiating any other sort of bargain about behavior.

Parents and children could decide how much use the children should make of the Internet, and the child should give his or her (5)____ that it won't interfere with homework. If the child is not holding to this arrangement, parents can take more drastic steps. Dealing with a child's use of the internet is not much different from negotiating any other sort of bargain about behavior.

Obviously, if children are bent over their computer for hours, (4)_____ in some game, instead of doing their homework, then something is wrong.

A surprising number of popular spectator sports, for example football or baseball, (1)______ in Europe or the USA in the nineteenth century. This did not happen by chance. It was the (2) ______ of changes in the way people lived in those places at that time. Until then, more people lived In the country than in towns. They worked in small groups and had no regular time off. All this changed with the growth of factories and industry in the nineteenth century, first in Europe and (3) ______. In the USA. For the first time, most people began to live in towns, and they found themselves with regular free time. They had more leisure time than ever before. This resulted in the need for organized entertainment. Suitable games developed or were invented, typically team games, in which the crowd could (4) ______ sides and become involved. This gave people some of the entertainment they need in their free time. The recent explosion in TV, with the introduction of satellite and cable channels, has caused an increase in (5) ______ for sports as entertainment. The money TV has broughtto games such as football, tennis and baseball means that spectator sports will certainly go on playing an important part in our lives.

Should parents worry if their children are spending that much time (3)_____ their computer?

The development of writing (1) ______ a huge difference to the world and might see it as the beginning of the (2) ______. Pieces of pottery with marks on that are probably numbers have been discovered in China that date from around 4000 BC. Hieroglyphics and other forms of "picture writing" developed in the (3) _______ around Mesopotamia (mordern-day Iraq), where the ancent Sumerian civilization was based, from around 3300 BC onwards. However, the first (4)________ alphabet was used by the Phoenicians around 1050BC. Their alphabet had 22 letters and it is estimated that it lasted for 1000 years. The first two signs were called "aleph" and "beth", which in Greek became "alpha" and "beta", which gave us the (5) ________ word "alphabet".

Any change in one part of an ecosystem can cause changes in other parts. Droughts, storms and fires can change ecosystems. Some changes harm ecosystems. If there is too (1)____ rainfall, plants will not have enough water to live. If a kind of plant dies off, the animals that feed on it may also die or move away. Some changes are good for ecosystems. Some pine forests need fire for the pine trees to reproduce. The seeds are sealed inside pinecones. Heat from a forest fire melts the seal and lets the seeds (2)_____. Polluting the air, soil, and water can harm ecosystems. Building (3)_______ on rivers for electric power and irrigation can harm ecosystems around the rivers. Bulldozing wetlands and cutting down (4)________ destroy ecosystems. Ecologists are working with companies and governments to find better ways of catching fish, cutting down trees, and building dams. They are looking for ways to get food, lumber, and other products for people (5)________ causing harm to ecosystems