肿瘤放射免疫显像的主要特点是（）

A.特异性强

B.灵敏度高

C.费用经济

D.简便易行

E.解剖定位准确

—Two hundred of the tourists were saved from danger in Taiwan, but the rest ______ still missing.  

—If the travel agency ______ more safety measures, this accident could have been avoided.  [ ]

A. is; has taken

B. are; had taken

C. were; had taken    

D. are; would take