Read the following passage and mark the letter A, B, c, or D to indicate the correct answer to each of the questions.

     Desert tundra, or cold desert, occurs on the Arctic edges of North America, Europe, and Asia. The word tundra comes from a Finnish word tunturia, which means barren land. In the desert tundra, the temperatures are almost always freezing, and they cause an environment in which plant life is virtually impossible. Plant life is made impossible by two different extreme conditions, either a lack or an overabundance of water.

     During at least three quarters of the year, the Arctic is frozen. The Arctic is far from the equator. This means the sunlight reaching the soil contains less energy than at the equator. The existence of ice rather than water for the majority of the year means that vegetation does not have enough moisture for growth to take place.

     During the period of time when the temperature increases enough for ice to melt, there is generally a large volume of water. Too much water and not enough drainage through the frozen subsoil make it difficult for plants to grow. Despite this, about 1,700 kinds of plants grow on tundra, including reindeer mosses, liverworts, and grasses. The 400 varieties of flowers found add a wide range of colors.

Which of the following is the best title for the passage?