It was so quiet in the classroom that a needle _____ to drop onto the floor. [ ]

A. could hear

B. was to be heard

C. could have been heard

D. must be heard

男，56岁，因急性腹痛诊断为"急性肠梗阻"，入院时血压60/40mmHg。急诊处理原则包括（）

A.非手术内科保守治疗

B.立即外科手术治疗

C.积极内科治疗，病情好转后择期手术治疗

D.积极抗休克，血压稳定后紧急手术

E.边抗休克边手术治疗