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Unit 4 READING 2

D inosaurs died because they could
not live in cold weather. But some
animals did live. They were mammals.
Mammals were very different from
dinosaurs. Mammals were warm-blooded.
Their bodies made heat. So, they could
live in colder weather. Dinosaurs were cold-blooded. Their bodies did not
make heat. So, they died in cold weather.

Mammals were different in other ways too. Mammals had bigger brains
than dinosaurs. They were much smarter. This was very helpful. Dinosaurs
could not change with the world. Mammals were smart. They found new
ways to live.

Mammals only had one problem. Cold-blooded animals can go for a long
time without eating. This is not true with warm-blooded animals. They had
to constantly find food. So, mammals moved around much more than
dinosaurs. Soon, mammals were all over the Earth.

English Usage

• different from ~
Apes are very different from humans.

• can[can’t] ~ without ...
The pain can go long without proper treatment.

120 Chapter 5 Science