题目内容：

Even if trees cannot walk, they are still on the move.

In parts of the Arctic, entire forests are moving northward. Across the Arctic, temperatures are rising faster than anywhere else in the world. As that happens, the tree line that marks where forests stop and the treeless tundra(冻原) starts has been moving northward. Trees growing along the tree line must protect themselves from the cold wind. To do this, plants tend to grow horizontal(水平的) branches low to the ground. The energy it takes for trees to grow this way means they don’t have enough energy to make seeds.

But as Earth’s climate has been warming, trees no longer have to just grow horizontally. Many can instead grow up toward the sky. This takes less energy. This happens especially in places where white spruce(白云杉) grows. White spruce, which is a North American trees, is quite able to produce a lot of seeds, which can move long distances in the wind. When wind-blown seeds end up on the tundra beyond the tree line, they finally sprout(发芽) new trees. This explains how a forest can move. Of course, the process would work only if the tundra were warm enough. But in recent years, the whole planet has been warming.

New trees will provide shelter for some snow. Keeping the sun’s rays from making the white surface disappear. Instead, the trees absorb(吸收) the sun’s heat. This warms the air around. The extra warmth encourages even more trees to produce seeds. That further increases a forest’s ability to expand(扩展). What’s more, more trees will trap more snow, preventing much of it from being blown away. Snow can trap heat in the soil below, which encourages trees to grow. The recent rise of temperatures has helped more trees grow past the tree line. People worry about effects on the animals that depend on frozen conditions for food and shelter.

1.What is the main cause of the trees in the Arctic moving northward?

A. The reducing of northern tundra.

B. The rising temperature.

C. The cold and strong wind.

D. The rich resources in the north.

2.What does the underlined word “this” in Paragraph 2 mean?

A. To produce more seeds.

B. To move northward.

C. To respond to the climate change.

D. To protect themselves from the cold wind.

3. What can be inferred from the last paragraph?

A. New trees can trap the snow, which may make the soil colder.

B. The trapped snow prevents new trees from producing more seeds.

C. New trees can make the air around warmer.

D. New trees can bring more food and shelter to local animals.