妈妈轻拍婴儿的背让他安静下来。

The mother patted the baby's back to ___quiet him down.

妈妈轻声哼唱摇篮曲来安抚哭闹的婴儿。

The mother softly hummed a lullaby to ___quiet the crying baby.

婴儿睡着后，房间里的噪音逐渐减弱了。

The noise in the room gradually ___quieted after the baby fell asleep.