题目

A sharp sword was found buried together with the royal carpenter, which was believed _____himself  against grave robbers.     A. used to defend   B. being used to defend  C. to be used to defending  D. to be used to defend   答案：D如图所示，在竖直光滑墙面上用细线系着一个重为G的小球，悬线与竖直墙面间的夹角为θ，则绳对球的拉力T及墙面对球的弹力N分别为 [　　] A．T=Gcosθ，N=GtanθB．T=Gcosθ，N=Gsinθ C．，N=GsinθD．，N=Gtanθ