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. -3II. 1III. 5
Ionly
IIonly
Iand II only
IIand III only
I,II, and III
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t + 2 is in the set,断定了只能向后推不能向前推,无法断定t-2是否一定存在在集合里
t + 2 is in the set,断定了只能向后推不能向前推,无法断定t-2是否一定存在在集合里
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