阿基米德蜗杆的模数m取（）值为标准值。

—When is Jack going to finish writing that program?

—I don't know ______ day in and day out.[ ]

A. He has been working

B. He has worked

C. He had been working

D. He was working

灯丝发射电子特性曲线是（）。

A.一定管电流下

B.一定管电压下

C.一定照射时间下

D.管电压与管电流之间的关系特性

E.管电流与灯丝加热电流之间的关系特性

高压水泵的启动程序。

短波接收机天线接收的SSB接收信号经（）送至HFRx单元。

A、馈线

B、多路耦合器

C、地线

D、传输导线

企业接受的投资者以原材料投资，其增值税额不能计入实收资本。 ( )