单选题 What is the main idea of the first two paragraphs?

A、 Green plants are very important to dry places.
B、 Land is becoming desert faster than scientists can change it back into good land.
C、 If scientists can bring water to desert, people can live and grow food there.

【正确答案】 B

【答案解析】[分析] 从前二段可以概括出来前两段的主要思想为B项内容。