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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为什么不能倒推?
为什么不能倒推?
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