If you come，you must be prepared to keep moving，______ it is too cold to stand and watch for long.[ ]

A．as  

B．when

C．if  

D．unless

颈总动脉、颈内静脉、迷走神经位于（）。

A.咽后隙

B.颈动脉鞘

C.颌下隙

D.舌下隙

E.咽旁隙