— Hello, I ____ you ____ in London, how long have you been here?   

— I came here last week.  [ ]

A. don't know; were    

B. didn't know; were

C. haven't known; are  

D. hadn't known; are  

图示等边角钢制成的悬臂梁AB，c点为截面形心，x′为该梁轴线，y′、z′为形心主轴。集中力F竖直向下，作用线过角钢两个狭长矩形边中线的交点，梁将发生以下变形：().

A．x′z′平面内的两面弯曲

B．扭转和x′z′平面内的平面弯曲

C．x′y′平面和x′z′平面内的双向弯曲

D．扭转和x′y′平面、x′z′平面内的双向弯曲