题目

 In recent years, China and the USA have had a lot of _________of views about the same problem. A．replacements    B．transformations   C．changes  D．exchanges 答案：D（本题满分14分）已知，且以下命题都为真命题：命题 实系数一元二次方程的两根都是虚数；命题 存在复数同时满足且.求实数的取值范围.