题目

The number of traffic accidents that _______ in developing countries _______ increasing. A. happen; is     B. happens; is      C. happens; are      D. happen; are 答案：A6．已知a+b=12，ab=9，且a＞b，则$\frac{\sqrt{a}+\sqrt{b}}{\sqrt{a}-\sqrt{b}}$的值为$\sqrt{3}$．