题目

 ______wants to make friends with ______people. They always thinks of themselves. A. Nobody; stubborn                     B. Everybody; easy-going C. Nobody; selfish                       D. Anybody; clever 答案：C某气象雷达发出的电磁波，频率是6.0×109Hz，该电磁波在真空中的波长是（　　）A．1.8×1018mB．20mC．0.50mD．0.05m