1. stop第三人称单数stops.用于一般现在时。He often stops to have a rest when he is tired.
2.stopping用于现在进行时。He is stopping at the red light now.
3.stopped用于一般过去时。He stopped to have a look at the yellow ducks.对各种时态的用法要明确。
stop为规则变化。所以，stop的过去式为：stoped；stopedstop的现在分词为：stopping
