题目

Don’t touch the book, Sally. You _____ more than one time.             A. warned        B. are warned    C. have warned   D. have been warned   答案：D等质量、等质量分数的稀硫酸和氢氧化钠溶液混合后，滴入紫色石蕊试液，溶液所呈的颜色是（　　）A．紫色B．红色C．蓝色D．无色