—Can you imagine Mike             across the Atlantic within a single day?

—We all imagine him         a brave and determined person.     [ ]

A. to sail; to be      

B. sailing; being

C. to sail; being      

D. sailing; to be

一般情况下，地铁内各种发热源产生热量的比例中，人员散发的热量大约占（）。

A.50%

B.5%

C.30%

D.15%