Our class teacher is still on ______ holiday, so our monitor will be in ______ charge of the meeting today.

A．/; /

B．the; the

C．a; /

D．the; a

迷走神经进入胸腔后在胸腔上部分出喉返神经，左侧喉返神经绕过________，右侧喉返神经绕过________，继而上行，行走于________，在________进入喉内。