阀门检修前应做哪些准备工作？

Woman: Your dormitory room isn't very large, is it Man: I can hardly turn around in it. Question: What does the man mean

A．His room is quite small.

B．He had to walk around the dormitory.

C．It's hard to find a room in the dormitory.

D．It's his turn to look at the dormitory room.

某公司计划投资建设一条新生产线，投资总额为60万元，预计新生产线接产后每年可为公司新增净利润4万元，生产线的年折旧额为6万元，则该投资的静态回收期为（）年。

A.5

B.6

C.10

D.15

下列哪种方法主要用于毒物分析

A．薄层色谱法

B．气相色谱法

C．高效液相色谱法

D．免疫分析法

E．分光光度法

货物搬运过程中损坏可能与包装材质有关。

当主蒸汽温度和凝汽器真空不变，主蒸汽压力下降时，若保持机组额定负荷不变，则对机组的安全运行（）。

A.有影响；

B.没有影响；

C.不利；

D.有利。