— That's the third time he's won the award in this field.   

— Yes. He ________ his maximum potential in the past decade. [ ]

A. explored          

B. is exploring  

C. has been exploring  

D. has explored

按雷诺数将流体分为（）三种流动状态。

A.层流区

B.过渡区

C.湍流区

D.对流区