题目

化简：3x2－5x一6－7x2－6x＋15 答案：3x2－5x–6－7x2－6x +15        =（3－7）x2+（－5－6）x +（－6+15）·············································· 1分 = －4x2－11 x +9················································································· 2分 下列现象中，你认为可称为反射的是：（   ） A．人一碰含羞草，其叶片马上卷起        B．摆在窗台上的花草向外生长 C．草履虫对环境中温度的变化表现出趋性 D．手偶然碰到火会迅速缩回