A:秦、唐
B:汉、宋
C:秦、明
D:明、清
Changes in our school
Number(in the past)
Number (now)
Classrooms
12
60
Students
590
1280
Library
0
1
Teachers’offices
6
15
Computer rooms
3
例:There were only 12 classrooms in our school, but now there are 60 classrooms.
在光滑水平面上有一物块始终受水平恒力F的作用而运动,在其正前方固定一个足够长的轻质弹簧,如图所示,当物块与弹簧接触后向右运动的过程中,下列说法正确的是( )