题目内容
--- Could you tell me why I am constantly yawning this afternoon?
---Yawning ______ an indication that your body lacks oxygen and needs a rest.
A. acts as B. serves as C. functions as D. plays as
C

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题目内容
--- Could you tell me why I am constantly yawning this afternoon?
---Yawning ______ an indication that your body lacks oxygen and needs a rest.
A. acts as B. serves as C. functions as D. plays as
C