He has worked in the factory _____ five years ago.[ ]
A. for
B. at
C. since
D. about
答案:C
下列哪种睾丸肿瘤不属于睾丸生殖细胞肿瘤。()
A.精原细胞瘤
B.间质细胞瘤
C.胚胎瘤
D.畸胎瘤
E.绒毛膜上皮癌
数据流图的类型有______和事务型。