粗糙的探测表面将导致（）。
A、缺陷回波幅度降低
B、接收脉冲宽度增加
C、盲区加大
D、上述都对
参考答案：D
—I missed the basketball game between Class 1 and Class 3 yesterday.
—Really?_________ It was great.
A. What a pity! B. Don’t mention it. C. I’m glad to hear that.
某企业为贫困山区孩子送温暖，共捐出衣物和棉被共1800件，已知衣物的件数比棉被件数的3倍少200件，则该企业捐的棉被有 件.
