1岁半男孩，股骨干上1/3斜骨折治疗最好采用

A．水平位皮牵引

B．水平位骨牵引

C．垂直悬吊牵引

D．切开复位内固定

E．石膏或夹板外固定

In the International Code of signals，a group of three letters indicates（）.

A.urgency or an emergency

B.the vessel's national identity signal

C.a group from the general signal code

D.a group from the medical signal code