Q26: If r, s, and t are positive integers, is r + s + t even? (1) r + s is even. (2) s + t is even.
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. 为什么答案是E,我觉得是C。 r + s is even 和s + t is even 所以r+s+s+t is even,r+t+2s=even,r+t=even-2s, r+t=even, r+t+s+t+r+s=even 2(r+s+t)=even, 则r+s+t=even,答案为c.请大n们帮忙解答阿！我什么地方推错了？ | 
