用如图所示的光电管研究光电效应的实验中，用某种频率的单色光a照射光电管阴极K，电

要除去密闭容器中空气里的氧气，得到较纯净的氮气可用燃烧法除氧气，下列物质中可选用的是（  ）

A．硫

B．木炭

C．红磷

D．蜡烛

This is a s__81____ of twin brothers, Justin and Paul. Their friend Susan calls them for h__82____. Justin and Paul drive to Hill Building q____83____. Three man in police uniform p___84___ them into a green van. They are not p__85_____. They are the robbers. The twin brothers aren’t a____86___. Paul opens the back door of the van w__87____ a knife. They take different r___88____ to the police station. They meet the robbers a____89__ in the police station. They are s____90_____. The policemen stop the van because the back door of the van is open.

为什么说遵义会议是中 * * 党历史上一个伟大的转折点

方向控制阀在用字母表示时，一般用字母（）表示右边的控制口。

A、Z

B、Y

C、P

试述φ400×290夹线缓冲垫的制作过程。