单选题 What is the main topic of the conversation?[A] The conversion of volcanic waste to fertilizer.[B] The menace of currently dormant volcanoes around Mount Saint Helena.[C] The eruption of Mount Saint Helena and its effects on the environment.

【正确答案】 C

【答案解析】[听力原文]16-20 M: The volcanic ash from the eruption of Mount Saint Helens certainly caused a lot of damage, didn't it? W: It did, but not as much as experts had predicted. It seems to have had a beneficial effect as well. M: Really? But were crop losses great? W: Yes, However, since the weather following the eruption was unexpectedly good, some crop yields remained steady or even increased beyond normal expectancy levels. M: I'm glad to hear that. But what was the beneficial effect you mentioned? W: A mass destruction of various insect populations. M: How could the ash kill insects without effecting people too? W: It's highly abrasive and quickly wears away the outer wax layer protecting insect bodies. Re- moval of that layer causes the insects to lose body moisture by evaporation, the result is usual- ly lethal. M: How about that? Sounds like an effective yet natural insecticide.

单选题 According to the woman, what was the extent of crop damage?[A] The crops were obliterated for the entire year.[B] The crops nutritional value was considerable lessened.[C] The loss was not as bad as had been anticipated.