A set of numbers has the property that for any number t in the set, t + 2 is in the set. If -1 is in the set, which of the following must also be in the set?
I.-3
II.1
III.5
I only
II only
I and II only
II and III only
I, II, and III
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t在set里,所以t+2在set里。 不能倒推
t在set里,所以t+2在set里。
不能倒推
不能倒退--嗯,学习了。。谢谢。那为啥答案是D?
t=-3 t+2=-1不成立 所以不能选1
多谢多谢
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