在下列实例中,不计空气阻力,系统机械能守恒的是( )
A:做自由落体运动的物体
B:小球落在弹簧上,把弹簧压缩后又被弹起
C:沿光滑曲面自由下滑的物体
D:起重机将重物匀速吊起
Now everybody, please turn to Page and look at the picture.
The Internet is very useful. We can get a lot of ________ from it.
关于日本的叙述,错误的是( )