请教GWD1-10,为什么-3不可以呢？

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.   I

III.   5

Why  -3 cannot also be in the set since t+2 is in the set? From my point of view,-1's in the set  indicate that -3 is also in it.

Is there sth wrong with my logic?

Please help me!

你可以理解该集合为 X=-1+2n,n>=0

所以X=-1,1,3,5,....

严格按照题干走，别多想

而且人家问的是“ must also be ”

不是could be，这个区别是相当大滴

明白啦

Thx a lot