因为22=2×2，所a2=a×2。[ ]
错误
用适当的介词填空。
1.I go to school ____ the morning.
2.Bill gets up ____ half past five every morning.
3.We don't have any lessons _____ Sunday.
4.We play football ____half _____ five in the afternoon.
5.- When is your English lesson?
- ____ seven.
如图，表面光滑的固定斜面顶端安装一定滑轮，小物块A、B用轻绳连接并跨过滑轮（不计滑轮的质量和摩擦）．初始时刻，A、B处于同一高度并恰好保持静止状态．剪断轻绳后A下落、B沿斜面下滑，则从剪断轻绳到物块着地，两物块（ ）
A．速率的变化量不同
B．机械能的变化量相同
C．重力势能的变化量相同
D．重力做功的平均功率相同
