— What an interesting book! Who wrote it?

— It            by Ben, my pen pal. [ ]

A. wrote

B. was written

C. was writing

D. is written

微分方程cosydx+（1+e^-x）sinydy=0满足初始条件y_x=0=的特解是：（）.

A．cosy=（1+e^x）

B．cosy=（1+e^x）

C．cosy=4（1+e^x）

D．cos²y=（1+e^x）