D-4：do duty for充当
A:Too hot! This summer's weather is abnormal.
A:太热了！今年夏天的天气不正常。
B:It's a pity that our classroom is not air-conditioned.
B：真遗憾教室里没有空调。
A:Air-condition? Are you dreaming? We even haven't a fan.
A：空调？你做梦呢？我们连台电扇都没有。
B:Maybe a book can do duty for a fan.
B：或许书本可代替风扇。
A:Yeah, We are so poor.
A:对呀。我们好可怜啊。
