—Why weren’t you at the meeting?

—I        for a call from my husband in Guangdong.

A．waited

B．had waited

C．was waiting

D．will wait

下列成分中，抗凝血作用最强的是

A．水蛭素
B．蚯蚓素
C．蚯蚓毒素
D．次黄嘌呤
E．琥珀酸