20121.       When Paul was a boy, _______.

A. he had decided never to leave his hometown

B. the economy of Utah depended wholly on the copper smelter

C. he hit a young visitor because of his comments on the wasteland

D. he stopped the copper smelter polluting the area

22.       Paul went to college to study the science of plants, because _______.

A. he wanted to find out the best way to save the area himself

B. he was interested in planting trees since he was young

C. he wanted to get more knowledgeable people to help him

D. he thought his knowledge would make his advice more convincing

23.       What does the underlined phrase “the plain common sense” probably mean?

A. It was impossible for trees to grow on the wasteland.

B. His normal work and life would be greatly affected.