Definition: the ground at the bottom of the sea, a river, etc. Level: C2
海床是多样海洋生物的家园。
The sea ___bed is home to diverse marine life.
他们倒栽在河床上，几乎所有人都在坠落中丧生。
They landed upside down on a river ___bed and almost everyone was killed during the fall.
水位下降时，湖底显露出来。
The ___bed of the lake was visible when the water level dropped.
