熔体泵运行时轴封保持微漏的原因是什么？
参考答案：
①保持轴封处润滑，防止迷宫密封磨损；
②防止外界空气漏入熔体泵内，造成粘度波动或影响产品质量。
The man we followed suddenly stopped and looked as if ______ whether he was going in the right
direction. [ ]
A. seeing
B. haying seen
C. to have seen
D. to see
以以Fletcher指数作为标准，临床检查病人诉听近距离谈话有困难，听阈可达60dB者，其耳聋分级应为（）
A.轻度耳聋
B.中度耳聋
C.重度耳聋
D.全聋
E.上述都不是
