“鹰击长空，鱼翔浅底，万类霜天竞自由”，这句诗中描述的生物生存的环境是（　　）

A．浅底、霜天

B．长空、浅底

C．长空、浅底、霜天

D．长空、霜天

When they awoke the next morning, they were surprised to find a ___ of fog floating in the air. [ ]

A. cover  

B. blanket  

C. piece  

D. mixture