----Look at the boy running on the playground. Is it David?

---- It ______ be him. I saw him go to the teachers’ office just now.

A．mustn’t

B．can’t

C．may not

D．needn’t

骨折急救处理时，下列哪项是最重要的（）.

A.立即复位固定

B.清洁裸露骨折端

C.简单妥善固定患肢

D.都需使用止血带

E.清洁伤口后固定患肢