上蜡操作时最好能将（）放在最后处理。
A、行李箱盖
B、翼子板
C、车门
D、发动机罩
参考答案：D
Not until all the fish died in the river ______ how serious the pollution was.
A．the villagers did realize
B．the villagers realized
C．did the villagers realize
D．didn’t the villagers realize
下列属于激素第二信使的是（）
A.DAG
B.cAMP
C.cGMP
D.IP3
E.Ca2+
