界限破坏时，正截面受弯承载力达到最大值。

一束太阳光垂直照到水平地面上，小明想利用平面镜反射的太阳光观察一个呈水平方向的小洞内的情况，则平面镜与水平面所成的锐角的度数为[ ]

A.45°

B.60°

C.70°

D.80°

A rich man was near death and was very upset. He had worked so hard for his money ______ he dreamt he could take it with him to heaven.So he ______ (祈祷) to God his dream would come true. An angel appeared and said no. The man begged the angel to speak to God to see whether he might ______ the rules. The angel reappeared and said that God could permit him to take one suitcase. ________(激动), the man gathered his suitcase and filled it with pure gold bars. Afterward, he died and showed up in heaven to greet St. Peter. S      the suitcase, St. Peter said，“Hold ______，you can't bring that here!” The man explained that he had God' p     . St. Peter checked it out    and said，“You are right. You are allowed o      suitcase, but I'm supposed to check its contents _______letting it through.” Inspecting the things that the man found too p      to leave behind, St. Peter exclaimed，“You brought pavement? As you can see , the street of heaven is made of gold!”

读“七大板块示意图”，完成下列内容：

①写出下列板块的名称

A______B______C______

D______E______ F______

②板块学说认为，各板块______地壳比较稳定，板块与板块______地带，地壳比较活跃．板块运动导致地球表层有的地方______，有的地方______．

- ______ he _____ on the farm(农场)?

-Yes, he does. He's a good farmer.[ ]

A. Does, work    

B. Is, working    

C. Does, do

简述成本控制的原则。