题目

What I learn about this violence is ________ it has caused at least three deaths. A . whether B . that C . what D . when 答案：B已知曲线C1：x=2cosθy=sinθ（θ为参数）与曲线C2：x=ty=kt-2（t为参数）有且只有一个公共点，则实数k的取值范围为 ．