清晨的鸟儿在树梢上欢快地歌唱。
The birds ___warble cheerfully in the treetops at dawn.
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.
鸟儿在枝头欢快地颤声歌唱。
The bird ___warbles cheerfully on the branch.
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