-How come your father can read books in German?

-Well, he _______ on a project with some German engineers for 3      years when he was young.   [ ]

A. worked               

B. has worked        

C. had worked      

D. would work

扫描电镜下T细胞急淋的原始淋巴细胞表面结构特点是（）

A.高而窄的嵴样突起

B.相对光滑或出现短微绒毛

C.表面主要呈光滑型

D.出现长而多的微绒毛

E.以上都不是