题目

All________ made________ possible for China to succeed in carrying out its open and reform policy. A . that happened; it B . what happened; it C . what happened; that D . that happened; that 答案：A7、如果对任意实数x，二次函数y=ax2+bx+c的值都是正数，那么有（　　）A、a＞0，b2-4ac＜0B、a＜0，b2-4ac＜0C、a＞0，b2-4ac＞0D、a＜0，b2-4ac＞0