练习：
1. Why did older volcanic eruptions do more damage than more recent ones?
A) Because they killed off life more easily.
B) Because they were brighter.
C) Because they were larger.
D) Because they were hotter.
2. How did Wignall calculate the killing power of those older volcanic eruptions?
A) By estimating how long they lasted.
B) By counting the dinosaurs they killed.
C) By studying the chemical composition of lava.
D) By comparing the proportion of life wiped out with the volume of lava produced.
3. When did dinosaurs become extinct?
A) 300 million years ago.
B) 250 million years ago.
C) 60 million years ago.
D) 65 million years ago.
4. What can be inferred from paragraph 3 concerning dinosaurs?
A) They were killed off by an asteroid.
B) They died of drastic climate change.
C) They were wiped off by a volcanic eruption.
D) The cause of their extinction has remained a controversial issue.
5. What is the main thesis of the article?
A) Volcanic eruptions are not always deadly.
B) Older volcanic eruptions were more destructive.
C) Carbon dioxide emissions often give rise to global warming.
D) It is not easy to calculate the killing power of a volcanic eruption.