TT31-1-10

TT31-1-10

Q10:

A set of numbers has the property(性质) 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:  D

答案是D，我看了一下讨论：根据提议只要把-1加上2(无限制次数)极为答案.-1+2=1, 1+2=3, 3+2=5,所以1和5都在数列里. 这个我能理解

但
                    -3 +2 = -1 不是吗?  所以应该这三个数都有包括在内吧?

A set of numbers has the property that for any number t in the set, t + 2 is in the set.

没有讲t=-5啊，所以-3不可