Millions of years ago, horses had many toes(脚趾). They had four toes on each front foot and three toes on each back foot. The horses were no bigger than cats.

       These small horses lived in the forest. Their toes helped them run over the soft, wet ground. It was very hot in the forest. But the weather gradually(逐渐地) changed. It became colder and colder, many trees could not live in cold weather. They died and fell, and open fields took the place of forests, the sun made the ground dry and hard.
       Horses began to change, too. They began to get bigger. This took a long, long time, on the dry and hard land. Horses needed only their middle toe for running. Their middle toes became hard. After a long while, horses had only one hard toe on the foot.
【小题1】Millions of years ago, the horse had four toes on each of its ________.

A．left feet

B．right feet

C．back feet

D．front feet

【小题2】Why couldn’t many of the trees live in the forest?

A．Because the ground was dry and hard.

B．Because the weather became colder and colder.

C．Because it was very hot.

D．Because the horse lived in it.

【小题3】From the story we know that ________.

A．the weather never changed

B．cats were once much bigger than horses

C．animals have always been the same as they are today

D．horses have changed a lot in the past millions of years