题目

73. --- You just think of yourself! You kept me waiting for at least three hours.    --- I’m sorry that you _____ think so.   A. will        B. would        C. should        D. Could 答案：C19．已知函数$f（x）=\left\{\begin{array}{l}{x^2}-1，x≤0\\ 3x，x＞0\end{array}\right.$，若f（x）=15，则x=（　　）A．4或-4或5B．4或-4C．-4或5D．4或5