The meeting had been on for half an hour _______ Miss Yang turned up.

A．while

B．As

C．Unless

D．before

口服避孕药期间若需怀孕，为避免药物影响而应在停药多长时间后受孕为妥

A．5个月后

B．2个月后

C．6个月后

D．4个月后

E．3个月后