Aborigines' most common tool in Australia is ________ boomerang, which is used to kill ________ animals.

A．the;/

B．/;/

C．the; the

D．/;the

小儿的第一个条件反射是()

A．拥抱反射

B．握持反射

C．吸吮反射

D．觅食反射

E．生后2周左右，抱起喂奶时出现吸吮动作