- Could you tell me why I am constantly
题型：选择题
问题：
- 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
- 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