— What did you say to Julia? I saw her crying in the dormitory alone.

— It _____ my fault. We talked happily when I was with her in the classroom.  [ ]

A. must have been

B. should have been

C. shouldn't have been

D. can't have been

下列哪种病原体引起的盆腔炎是以血行传播为主

A．大肠杆菌

B．葡萄球菌

C．沙眼衣原体

D．淋病奈瑟菌

E．结核杆菌