题目

 ____ students should be given more free time is suggested by many experts and welcomed by kids in school. A. What       B. Why          C. Whether     D. That 答案：D已知不等式x+2x+1＜0的解集为{x|a＜x＜b}，点A（a，b）在直线mx+ny+1=0上，其中mn＞0，则2m+1n的最小值为 ．