作图题：请画出事故音响试验回路。
参考答案：
见图E-74
228. Now more and more people prefer to have a ______ at home --- a little dog, a cat or some other animals.
A．habit
B．hobby
C．parrot
D．Pet
“高钙奶粉”是指该奶粉中富含“钙”
A．单质
B．元素
C．原子
D．分子
