-Let's go to Hainan on vacation.

-Oh, no. I have         to Hainan several times.

A．got

B．come

C．been

D．gone

下面哪几个解剖结构组成颈动脉三角的边界（）

A.胸锁乳突肌前缘

B.二腹肌前腹

C.二腹肌后腹

D.肩胛舌骨肌上腹

E.颈前正中线