We all have enough time to do enough exercise to ____ ____.
下图分别是每天的哪个时段,为什么?
—At first I was excited, but later I got and left.
如图所示,电动势为E、内阻为r的电池与定值电阻R0、滑动变阻器R串联,已知R0=r, 滑动变阻器的最大阻值是2r.当滑动变阻器的滑片P由a端向b端滑动时,下列说法中正确的是( )
围成一个正方形做游戏,每边站15人,四个顶点都有人,最外层一共有( )人.