如图是我国各省级行政区水土流失面积图，读图完成下列要求：

    It's duty of every man to work. The life of a lazy man is of no use to himself and to others. If the man is too lazy to work, he will usually become a not useful man. Everyone, when he is young, should learn some useful work.
    But it's not enough for a man to learn some kind of work. He should put his heart and soul (精力) into his work, and not waste his free time. “Work while you work and play while you play” is as good rule for young people as old.
    There is no better to help to diligence than the habit of early rising, and this, just like all other good habits, is most easily formed in youth (青年). There is an English say “Lost time never returns.” This means that everybody must be diligent, and make good use of time. One must study hard when one is young so that one can make great progress, succeed in life and become useful to one's country. So we can say that diligence is the mother of success.

如图所示，磁场与线圈平面垂直，先后以速度v₁和v₂匀速把一矩形线圈拉出有界匀强磁场区域，v₁=3v₂．在先后两种情况下（   ）