While I_________that he is an excellent leader,I don’t think he can do a good job in this company because he is too careless.

A．reflect

B．recommend

C．acknowledge

D．urge

三种平面应力状态如图所示(图中用n和s分别表示正应力和剪应力)，它们之间的关系是（）。

A.全部等价

B.a)与b)等价

C.a)与c)等价

D.都不等价