I can hardly imagine Peter ______across the Atlantic Ocean in five days.

A．sail

B．to sail

C．sailing

D．to have sailed

（）应力仪可用来检测所受的应力是否均匀。

A、镜片在磨边时

B、镜片在抛光时

C、镜片在镜架内

D、镜片在镜架外