用所给词的适当形式填空。

1. Kangaroos are _____ (play) and  chimpanzees are _____ (noise).

2. I was _____ (surprise) to find hardly anyone in the zoo.

3. Zoos are like _____ (live) textbooks for young people. 

4. He _____ (use) to be _____ (call) "Little Tiger".

5. Liu Xiang's success is an _____ (inspire) to us all.

巴甫洛夫的经典条件作用可解释（ ）

A．人的情感的学习

B．人的常识性知识的学习

C．人的信号学习

D．上述各项学习