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 Helens. C. The eruption of Mount Saint Helens and its effects on the environment.

【正确答案】 C

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