产毒性大肠杆菌肠炎的发病机制是（）
A.渗透性腹泻
B.分泌性腹泻
C.侵袭性腹泻
D.动力性腹泻
E.吸收障碍性腹泻
参考答案：B
I'm sorry you've been waiting so long, but it'll still be some time ______ Brian gets back. [ ]
A. before
B. since
C. till
D. after
应答器编号045-1-23-004中045表示大区编号
