Q26:

K is a set of integers such that if the integer r is in K, then r + 1 is also in K.  Is 100 in K?

(1)     50 is in K.

(2)     150 is in K.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

问什么是a呢？解释一下？

（1）如果50在k里面那么51＝50＋1也在里面，那么52＝51＋1也在。。。。那么100也在。。。所以（1）对

（2）只知道大于150的都在，但不知道小于的在不在，所以（2）不行。