题目

She is _____ girl from Asia. A. a 18-year-old                B. an 18-year-old C. an 18-years-old              D. a 18-years-old         答案：B9．函数f（x）=$\left\{\begin{array}{l}{-x-1，x＜1}\\{（\frac{1}{2}）^{x-1}，x≥1}\end{array}\right.$的图象与函数g（x）=log2（x+a）（a∈R）的图象恰有一个交点，则实数a的取值范围是（　　）A．a＞1B．a≤-$\frac{3}{4}$C．a≥1或a＜-$\frac{3}{4}$D．a＞1或a≤-$\frac{3}{4}$