题目

已知函数f(x)=ax2+bx-1(a,b∈R且a＞0)有两个零点，其中一个零点在区间（1，2）内，则a-b的取值范围为      （    ）      A．（-1，1）                                      B．（-∞，-1）             C．（-∞，1）                                               D．（-1，+∞）短文改错假设英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的以下作文。文中共有10处语言错误，每句中最多有两处。错误仅涉及一个单词的增加、删除或修改。增加：在缺词处加一个漏字符号(∧)，并在其下面写出该加的词。删除：把多余的词用(＼)划掉。修改：在错的词下画一横线，并在该词下面写出修改后的词。注意：1.每处错误及其修改均仅限一词；2.只允许修改10处，多者（从第11处起）不计分Ladies and gentlemen,Welcome to our English Corner. This Corner was set up three years before. Every Sunday morning, students from different schools and some foreigners often took part. Gather around here, we practise spoken English by talking about everything we are interested. We also exchange my experience in English study. We all have a good time here. Thousands of people have been here when it was set up.We think that they have learned a lot by talking part in activity here. It is a really supplement to our English class and it is welcomed by students, their parents and teachers. They all think it is of helpful. If you want to know much about the corner, you may talk to the students here.