“唉！这家人真够惨了。”中的“唉！”是（）。
A.独立成分
B.非主谓句
C.分句
D.词
参考答案：B
68. The Summer Palace is one of the _____ parks in Beijing. I suggest you going there to have a visit.
A．more beautiful
B．most beautiful
C．best beautiful
D．much beautiful
当压力达到设定值时，（）动作将流体卸到低压容器或管线从而将压力降低到安全值以内
A、关断阀
B、压力安全阀
C、放空阀
D、排空阀
