当空气预热器严重堵灰时，其入口烟道负压增大，出口烟道负压减小，炉压周期性波动。（）
参考答案：错
Doctors are often caught in a ________ because they have to decide whether they should
tell their patients the truth or not.[ ]
A. puzzle
B. dilemma
C. trouble
D. difficulty
出现瘘管试验阳性的情况是（）。
A.听骨链中断
B.膜迷路积水
C.外淋巴瘘
D.听骨链固定
E.死迷路
