题目

你向朋友介绍你的弟弟，你会说：________ A . This is my father. B . This is your brother. C . This is my brother. 答案：C18．已知0＜a＜b，且a+b=1，则下列不等式中，正确的是（　　）A．log2a＞0B．2a-b$＜\frac{1}{2}$C．log2a+log2b＜-2D．2${\;}^{\frac{b}{a}+\frac{a}{b}}$$＜\frac{1}{2}$