为什么要进行锅炉汽水系统严密性试验？

伴三凹征的呼吸困难，出现于下列哪种情况（）

A.呼气性呼吸困难

B.吸气性呼吸困难

C.神经官能症

D.中毒性呼吸困难

E.脑膜炎

A new study suggests that the more teenagers watch television,_______ develop depression(抑郁症) as young adults.

A．the more likely they are to

B．the more likely they are

C．they are the more likely to

D．the more likely are they

测量用互感器的主要类型有哪些？

循环骤停的临界时间是（）。

A.1min

B.2min

C.4min

D.8min

E.10min

水蒸气分解成同温度的氢气和氧气，内能增加了（）。（不计振动自由度）

A．0

B．25%

C．50%

D．66.7%