Millions of years ago dinosaurs (恐龙) lived on the earth. In the days of dinosaurs the whole earth was warm and wet. There were green forests and they could find enough to eat. Later, parts of the earth became cold and dry. and the forests there died. Then dinosaurs could not find enough to cat. This must be one reason why dinosaurs died out.
We can guess another reason. New kinds of animals came on the earth. Some had big brains and were fast and strong. They could kill dinosaurs. There may be other reasons that we don’t know about yet. Scientists are trying to make more discoveries about dinosaurs.
Dinosaurs were of many sizes and shapes (形状).  Some were as small as chickens, while some were about 90 feet long.
There were also terrible fights between dinosaurs. They might have happened more than 100 million years ago. Though there was no man to see any of the fights, we can be told by the animal’s footprints (足迹) that fight did take place.
According to the passage, dinosaurs did exist only ______on the earth.

A．for millions of years

B．millions of years ago

C．more than 100 millions years ago

D．when it was warm and wet somewhere

  One reason why dinosaurs died out is that______.

A．there were too many dinosaurs

B．parts of the earth became cold and dry

C．the dead forests there could not supply them with enough food

D．they couldn’t find enough to eat

. One more reason may be that ______.

A．new kinds of animals came on the earth

B．some fast and strong animals with big brains could kill them

C．some dinosaurs were as small as chickens

D．some big dinosaurs died in the fights

We can see from this passage ______.

A．scientists are trying to make some dinosaurs

B．dinosaurs are dangerous enough

C．dinosaurs are worth studying

D．scientists know nothing about dinosaurs