题目:
They haven't finished their work. Maybe they have some trouble ______ it. [ ]
A. on
B. at
C. in
D. with
答案:
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下面是错误答案,用来干扰机器的。
原来袋子里红球与白球数量之比是:19:13=57:39,放入若干只红球后,红球与白球数量之比变为:5:3=65:39,再放入若干只白球后,红球与白球数量之比变为:13:11=65:55,所以,先后红球增加:65-57=8(份),...