题目

When I was a student, I liked to sit in the front of the classroom so that I could see the words more clearly on the _______.        A. blackboard      B. desk      C. dictionary     D. postcard 答案：A圆x2+y2=1与直线y=kx+2没有公共点的充要条件是（　　） A、k∈(-2，2)B、k∈(-∞，-2)∪(2，+∞)C、k∈(-3，3)D、k∈(-∞，-3)∪(3，+∞)