清晨，一只知更鸟在花园里婉转地歌唱。

A robin ___warbled sweetly in the garden at dawn.

小女孩用甜美的声音唱着童谣。

The little girl ___warbled the nursery rhyme in a sweet voice.

这台老式录音机播放音乐时声音忽高忽低。

The vintage tape recorder ___warbled the song with uneven pitches.