用于药物的各种溶媒，启封后超过多少时间不得再使用
A．4小时
B．2小时
C．24小时
D．48小时
E．8小时
参考答案：C
After a knock at the door, the child heard his mother’s voice ____ him. [ ]
A. calling
B. called
C. being called
D. to call
列当的危害是什么？如何防治？
