A.cook
B.wood
C.boot
D.childhood

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 rewar

A．throwing stones often caused injuries
B．throwing stones was not fun
C．games with stones did not have rules
D．rocks were too heavy to throw