题目

 ________, I think, and the problem could be settled. A. A bit more effort         B. So long as you keep up your spirits C. If you doubt your efforts   D. Making great efforts 答案：A请写出一个二次函数，使它同时具有如下性质：①图象关于直线对称；②当x＝2时，y＞0；③当x＝－2时，y＜0．答：           ．