这个题，我认为答案是E就是都有，可是给的答案是D能帮我解释一下吗？

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

A.    I only

B.    II only

C.    I and II only

D.    II and III only

E.    I, II, and III

Answer:

----------------------------------------------------------

对阿

1=-1+2

5=-1+2+2+2

没有说可以向前推，所有不知道-3是否也在这set中阿