In Mr Kim's fish tank, every fish is either orange or white. None of the orange fish has stripes.
Dot is a fish in Mr Kim's tank, and Dot has stripes. Which one of these must be true?
AA.
Dot is a white fish.
BB.
Dot is an orange fish.
CC.
Every white fish in the tank has stripes.
DD.
Dot is the only fish in the tank with stripes.
答案: A
答案:A(Dot is a white fish.)
鱼缸里的鱼不是橙色就是白色。
橙色的鱼都没有条纹。Dot有条纹,所以Dot不可能是橙色的。
剩下的颜色只有白色,所以Dot是一条白色的鱼。
为什么其他选项不对
B(Dot is an orange fish.):橙色的鱼没有条纹,有条纹的鱼不可能是橙色的。
C:我们只知道Dot的情况,有些白色的鱼可能根本没有条纹。
D:别的白色鱼也可能有条纹,题目并没有说只有Dot有。
讲解示例 2
There are 24 children in Ms Nguyen's class. Each child voted once for a class mascot: a koala, an emu or a platypus. The koala got more than half of the votes.
Which one of these must be true?
AA.
The platypus got at least 1 vote.
BB.
The emu got fewer than 12 votes.
CC.
The koala got exactly 13 votes.
DD.
The emu got more votes than the platypus.
答案: B
答案:B(The emu got fewer than 12 votes.)
24的一半是12,“超过一半”说明koala至少得了13票。
剩下给emu和platypus的票加起来最多是24 − 13 = 11票。
所以emu最多得11票,一定少于12票。
为什么其他选项不对
A(The platypus got at least 1 vote.):其余的票可能全投给了emu,platypus可能一票都没有。