GCr15SiMn是（）。

GCr15SiMn是(  )。

  A．高速钢  B．中碳钢

  C．轴承钢  D．不锈钢

A.15%

B.1.5%

C.0.15%

D.0.015%

请将下列牌号的金属材料进行分类：

  40，65，GCr15，H62，QSn4-3，ZChPb16-16-2，YG8，40Cr，W18Cr4V，20Cr

  ZG200-400，Y40Mn，60Si2Mn，5CrMnMo，20Cr，Cr12，HT100，LF5，ZAR

  3Cr2W8V。

  1．硬质合金   2．弹簧钢

  3．高速钢    4．铝合金

  5．灰．口铸铁  6．热作模钢

  7．调质钢    8．冷作模钢

  9．铸钢     10．青铜

  11．渗碳钢    12．轴承钢

  13．易切钢    14．黄铜

  15．巴氏合金

某数控机床的滚柱导轨的材料为GCr15轴承钢，淬火硬度为60HRC，滚柱长度l=20mm，直径d=8mm，每一导轨上所分担的运动部件的重力G=1200N，导轨硬度修正系数ξ=1，若使该导轨承受P_z=36000N的最大载荷，请计算该滚动导轨滚动体横截面上的应力Pz。

It is the firm belief of astronomers【C1】______there are living creatures on other planets. It is also their ear- nest wish that some day【C2】______may be made with such living creatures【C3】______sending messages in the form. of radio signals. The【C4】______of communicating with people on other planets may one day come【C5】______since radio telescopes【C6】______.

Scientific project of various kinds are now being launched to【C7】______signals or to receive signals from distant planets. The question now【C8】______: What sort of message【C9】______so that it could be understood? To send a message in any language would be impractical【C10】______it would【C11】______not be intelligible.

It is the opinion of scientists that a signal in the【C12】______of a simple arithmetic sequence might be understood.

Scientists think that pictures might also be understood, so it【C13】______a good idea to send pictures of the people【C14】______our planet. Pictures of domestic animals together with【C15】______crops we【C16】______for our food might also be【C17】______. Pictures of houses and buildings might【C18】______further information about our life and society.

As time goes on, TV pictures might be sent, which would【C19】______acquaint the beings on other planets【C20】______life and the level of civilization on our planet.

【C1】

A．which

B．what

C．why

D．that