刚做了一套GWD，有两个数学还是没思路。不好意思，一时搜不到前人的帖子，还请各位帮忙看看，月底考试了，急啊。
4,For a nonnegative integer n, if the remainder is 1 when 2n is divided by 3, then which of the following must be true?
I. n is greater than zero. II. 3n = (-3)n III. √2n is an integer.
A. I only
B. II only C. I and II
D. I and III
E. II and III
Answer: E
Q15: If n is a positive integer and r is the remainder when (n – 1)(n + 1) is divided by 24, what is the value of r? (1) 2 is not a factor of n. (2) 3 is not a factor of n. 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. Answer: C
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