题目

Heredity （遗传） is not the only thing that influences our color. Where we live and how we live after we are born are important too. For instance, our genes influence how fat or thin we are. But our weight depends mainly upon how much we eat and how much exercise we get. In the same way, our skin color depends to a large extent upon how much sunshine we get.        When summer arrives and light-colored people go to the beaches, some will tan darkly, some will tan lightly and few will not tan at all. Each one is born with a different ability to tan, but the differences do not appear 14．两个完全相同的条形磁铁，放在平板AB上，磁铁的N、S极如图所示，开始时平板及磁铁皆处于水平位置，且静止不动．（1）现将AB突然竖直向上平移（平板与磁铁之间始终接触），并使之停在A″B″处，结果发现两个条形磁铁吸在了一起．（2）如果将AB从原来位置突然竖直向下平移（平板与磁铁之间始终接触），并使之停在位置A′B′处，结果发现两条形磁铁也吸在了一起，则下列说法正确的是（　　）A．开始时两磁铁静止不动说明磁铁间的吸引力是静摩擦力B．开始时两磁铁静止不动说明磁铁有惯性C．（1）过程中磁铁开始滑动时，平板正在向上加速D．（2）过程中磁铁开始滑动时，平板正在向下加速