题目

求函数y=ln的导数. 答案：解：y=ln（x2+1）.y′=［ln（x2+1）］′=· （x2+1）′=.从所给的四个选项中选择最佳答案 We are sorry to hear that they didn't arrive on time, as ______. [　　] A．they asked　　　B．asked to C．asking for　　　D．asked then