---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 asB.serves asC.functions asD.plays as
网友回答
C解析这题考查词组function as“起什么作用”，acts as和serves as都是“担当…”句意是：--你能告诉我怎么一个下午我都在打哈欠。--打哈欠的作用是表明你的身体缺乏氧气，需要睡眠了。选C。