请教天山7-26

sunjueliang

K is a set of integers such that if the integer r is in the K,then r+1 is also
in K.Is 100 in K?
1.50 is in K
2.150 is in K
答案是 A,但我认为选D,(2)也对,{1,2,....100,...150...}是否也可以?

lemonees

选Ａ没有错的！

条件二只能推出150+1,150+2,150+3.....在数列里头，题目的已知并密有告诉我们可以倒推，所不充分！

observer

我也没什么好解释的了，就是不能倒着推，此处不能举一反三。[em01]