The correct answer is sing.
B. sing with trills
D. move unsteadily
The correct answer is (B) To sing with trills; to sing with long trills, runs or quavers like a bird. Also, to speak in a manner suggestive of bird's song.
Warble comes from Norman French werbler, Old High German werbel.
Examples of use:
- Throughout the afternoon, the canary warbled on its perch.
- She warbled a tune as she worked.