There have been many comparisons (比较) made between London Underground and New York Subway. They are the best known public transport systems (公共交通运输系统) in the world and each is a key part of one of the greatest cities of the world. The two systems have many things in common(相同), including their ages and fame（名声）, but there are also important differences.

    The following table shows some of the similarities (类似）and differences.

如图所示，两块水平放置的金属板距离为d，用导线、开关K与一个n匝的线圈连接，线圈置于方向竖直向上的变化磁场B中．两板间放一台小压力传感器，压力传感器上表面静止放置一个质量为m、电荷量为+q的小球，K断开时传感器上有示数，K闭合稳定后传感器上恰好无示数，则线圈中的磁场B的变化情况和磁通量变化率分别是（   ）

— What do you do on the weekend? — I ____ my room.