已知丙烷的二氯代物有四种异构体，则其六氯代物的异构体数目为（）
A.两种
B.三种
C.四种
D.五种
参考答案：C
最早的外科医师称为：（）
A.疾医
B.疡医
C.食医
D.兽医
E.大方脉
Not believing their eyes, the visitors on the spot _______ the flying plane, doing some most difficult and dangerous tricks in the sky.
A．glared at
B．stared at
C．glanced at
D．caught sight of
