细金属丝材涡流探伤，一般使用的探头型式为（）。

A.穿过式

B.内插式

C.旋转式

D.混合式

Usain Bolt________what he will be bringing to the audience as he prepares to defend his title in the

London Olympics.[ ]

A. is well aware of  

B. is well worth

C. is content with  

D. is satisfied with