I _____ that actress in quite a few films, but her name escapes me for the moment. [ ]

A. saw

B. have seen

C. see

D. had seen

骨肉瘤治愈率低的最主要原因是（）

A.肿瘤恶性度高

B.手术切除不彻底

C.肿瘤对化疗不敏感

D.患者不能坚持术后化疗

E.在诊断时已有70％的病人在血液中发现瘤细胞