常用于防治心绞痛急性发作的药物是
A．硝酸甘油
B．普萘洛尔
C．美托洛尔
D．硝普钠
E．硝苯地平
参考答案：A
Why the explosion occurred was ____the laboratory attendant had been careless.
A．for
B．because
C．since
D．that
DHCP服务器被动打开（），等待客户端发来的报文。
A、TCP端口67
B、TCP端口68
C、UDP端口68
D、UDP端口67
