________about the result of the experiment，he still wants to give it a try．

A．Uncertain as he is

B．As uncertain he is

C．As he is uncertain

D．Uncertain is he as

以头颅部或颈部作为抗基来移动牙齿或颌骨，此牵引为（）

A.Ⅱ类颌间牵引

B.Ⅲ类颌间牵引

C.颌间垂直牵引

D.颌内牵引

E.颌外牵引