Sorry, I don't know the answer ______ the question ______ it is too hard. [ ]

A. to, because

B. too, or

C. of, because

D. to, so

疑“胆总管结石”，应首选（）

A.口服胆囊造影

B.ERCP

C.低张十二指肠造影

D.肠系膜上动脉造影

E.腹部平片