GWD的第一套··q10

memolsh

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?
-3
1
5


A.    I only
B.    II only
C.    I and II only
D.    II and III only
E.    I, II, and III
但是当t+2=-1的时候，t=-3，为什么不行！！

lisaxiong

这道题的正确答案究竟是什么啊？