He said that he dropped his bag when he ______ for the bus.

a. was runing   b. was running   c. were running   d. is running

根据纵隔间隙器官的位置，按三区划分法，下列正确的是（）。

A.分为前、中、后三区

B.以气管、心包前方至胸骨的间隙为前纵隔

C.气管、心包后方，包括食管及脊柱旁为后纵隔

D.前后纵隔之间有多种重要器官的间隙为中纵隔

E.以上都是