以下是引用nolanchen在2006-8-3 11:58:00的发言：If k is a positive integer, is k the square of an integer? (1) k is divisible by 4. (2) k is divisible by exactly 4 different prime numbers. A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient. B. Statement (2) ALONE is sufficien t, 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. Answer: E
我觉得该选B啊?哪位NN指点迷津? B不对，选E 比如420有2 ，3，5，7四个不同的质因子（当然用数字验证时可以倒着算，先找4个最小的质因子，算起来比较方便）符合条件（2）， 也能被4整除，符合条件（1）， 但不是某个数的平方 所以是E。 应该是的。偶现在做了一些题，错误较多，有时都影响自信心了。 | 
