她把钥匙掉进鱼缸里，发出扑通一声。

She dropped the keys and they ___plopped into the fish tank.

他疲惫地走进房间，扑通一声躺在了床上。

He walked into the room tiredly and ___plopped down on the bed.

小石头掉进池塘时发出轻轻的扑通声。

The stone made a quiet ___plop as it fell into the pond.