a、b两物体的质量分别为m1、m2,由轻质弹簧相连(如图1).当用恒力F竖直向上拉着a,使a、b一起向上做匀加速直线运动时,弹簧伸长量为x1;当用大小仍为F的恒力沿水平方向拉着a,使a、b一起沿光滑水平桌面做匀加速直线运动时,弹簧伸长量为x2,如图2所示,则( ) A.x1一定小于x2 B.x1一定等于x2 C.若m1>m2,则x1>x2 D.若m1<m2,则x1<x26.Where does the conversation probably take place?A.At an airport B.In a restaurant. C.In a post office.