The young man stopped and looked back as if ______ whether he was being followed.

A．seeing

B．to have seen

C．having seen

D．to see

在体内，两药并用容易发生蛋白结合部位置换的药（）。

A.苯巴比妥，卡马西平

B.甲基硫氧嘧啶，多西环素

C.磺胺，甲磺丁脲

D.氯贝丁酯，华法林

E.对乙酰氨基酚，头孢氨苄