阅读短文，根据短文内容，判断下列句子的正误。

    Rules are like rulers they tell us what we should do. We use signs to talk about rules. There are four kinds of signs. They are warning signs, information signs, direction signs, instruction (指令)signs. We can find a 'No smoking' in the library. It means we mustn't smoke. We can find a 'No swimming' sign by a river or a pool. It tells us we can't swim here. An instruction sign tells us how to do or not to do something. A direction sign tells us where to go. Signs are very important for everyone. They tell us what we must or mustn't do. We should obey the signs. If there are no signs on the road, accidents will happen everywhere. So we should follow the signs.