The trees have been on the earth for millions of years.   Disease(疾病) is destroying trees. For example, in the 1970s, many trees in Europe were killed by disease.
 This new danger attacks all the forests and woods of Europe from northern Sweden to southern Italy. First the branches turn yellow and brown. Then the trees’ leaves fall. The roots and the trunk shrink(萎缩). Finally the trees die. In the Black Forest in southern Germany, 75％of the trees have been destroyed or killed．
 Nobody knows exactly, but it is probably air pollution or acid rain(酸雨). Factories, power stations and cars give off tons of smoke with acid into the air. Sunlight turns these into something harmful which fall with rain or snow onto the trees.
What can be done about acid rain? 
Acid rain doesn’t always fall on the countries which produce the pollution. The wind carries it from one country to another. Badly, the governments don’ t want to spend money on it if it won’ t harm the trees in their own countries.
 The rainforests of Asia and South America are being cut down for firewood and building materials. Something must be done. If the trees die, we will, too.
根据材料内容，从下面五个选项中选出能填入文中空缺处的最佳选项，使短文意思通顺，内容完整。

A．What is killing the trees?

B．But today trees are in great danger.

C．Trees are also killed by people.

D．Now an even greater danger is destroying trees.

E. Why don’t the governments do something to save the trees?