It took him a long time to ______the skills he needed to become a professional artist.

A．acquire

B．inquire

C．require

D．request

对环状软骨的叙述，正确的是（）。

A.位于甲状软骨的后方

B.由环状软骨弓和环状软骨板构成

C.环状软骨弓平对第4颈椎

D.有左、右2个软骨板

E.构成喉的前壁