验证金属的活动性顺序，一般通过两种途径：

如图所示，两根互相绝缘、垂直放置的直导线ab和cd，分别通有方向如图的电流，若通电导线ab固定不动，导线cd能自由运动，则它的运动情况是（   ）

    We can't live without love and we know what love is, but we don't say only humans know what love is. Yes, it's impossible for animals to do some things because of their physical body. However, sometimes some of them might be able to show us the love that we have forgotten on our "busy road", just like the following story.
    A dog, was knocked down by a car and died in the middle of the road. Later, another dog ran beside the body of the dead dog and he tried to wake his friend up using his legs. When his effort to wake up his friend failed, he tried to push his friend to the roadside. But his friend was too heavy for him to push.
    Though traffic was busy and dangerous, he wouldn't want to go away from his friend, just standing beside his friend shouting and crying.
    A lot of people saw this story and were very touched (感动的). Even a dog can show his loyalty (忠诚) and love to his friend, what can our humans do?

最小的五位数比最大的四位数多1.