Birds flew in and out of the tree, singing merrily.
Meaning: This sentence portrays the lively atmosphere around the tree, with birds flying in and out, adding to the beauty of the scene with their cheerful singing.
Choice of Words: Birds are warm-blooded vertebrates with feathers and wings. Flew means to move through the air using wings. Tree is a large woody plant with a trunk and branches. Singing means to produce musical sounds with the voice. Merrily means in a cheerful and carefree manner. When you put them together, "Birds flew in and out of the tree, singing merrily" creates a charming image of birds flitting around the tree, filling the air with their melodious songs.
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