Children are having a good time in the park.

A．have fun

B．enjoy themselves

C．having fun

D．playing games

下列关于口对口人工呼吸操作的叙述，不恰当的是

A．吹气时向后压环状软骨

B．头极度后仰，托起下颌

C．吹气要看到胸廓抬起

D．吹气不少于20次/分