食管的第一个生理狭窄在（）

A.起始处

B.穿膈处

C.与主动脉交叉处

D.与右主支气管交叉处

E.与左主支气管交叉处

Is that seat taken?（）

A.Please don't worry. 

B.I don't think so. 

C.Why not? 

D.It's very nice.