单项选择题
| Dinosaurs were reptiles which became
extinct about 65 million years ago. The most intriguing question about dinosaurs
has always been " (21) did they die out" There is no simple
answer to this question, (22) many hundreds of scientists are
studying the problem. They are not studying the extinction of the dinosaurs
(23) , but the whole question of extinction. Many other plants
and animals have (24) in the past, and it is important to
understand (25) this happened. Having this information could
help save many species that are (26) in the modern world.
Humans are causing extinctions now, because of pollution and other damage
(27) the environment. Maybe the dinosaurs can tell us how to
save the earth today, (28) their extinction 65 million years
ago! Some of the early dinosaur scientists, 100 years ago, thought the dinosaurs
died out because the (29) changed, and they could not
breathe. Others thought that the dinosaurs disappeared simply because they
became too big. They were (30) to move and could not find enough food (31) One theory is that a huge killer meteorite (32) the earth. Some scientists (33) that the extinction of dinosaurs was possibly due to rapid (34) of the planet’s climate. Perhaps huge amounts of lava pours out of volcanoes in India. This sent up vast (35) of dust that blacked out the sun, and made the earth icy cold. |