— Can I call you back at two o'clock this afternoon?                              

— I'm sorry, but by then I ________ to Beijing. How about five?[ ]

A. fly  

B. will fly

C. will be flying   

D. am flying

一个梯形有三条边都是4cm，另一边是8cm，那么这个梯形的面积是（    ）cm²．