【单选题】Can animals be made to work for us? Some scientists think that one day animals may be trained to do a number of simple jobs that are now done by human beings. They point out that at a circus, for exam...
A.
Animals are very skillful at a circus.
B.
They are big and strong.
C.
Some animals are as clever as human beings.
D.
Animals can be trained because they like to get something as a reward.