7.已知a＝$\ln {2}$，$b＝e - \frac{1}{a}$，c＝2a-a，则
A.b＞c＞a B.b＞a＞c C.c＞a＞b D.c＞b＞a
15.已知函数f（x）＝$\left\{ \begin{aligned} {e}^{ - 2x} - 1,x \leq 0, \\ \frac{1}{2}\ln {(x+1),x>0.} \end{aligned} \right.$ 若x（f（x）-a|x|）≤0，则a的取值范围是.