Cars were very few and only rich people could buy them.

题目

Cars were very few and only rich people could buy them.
However,in England cars were thought to be dangerous at that time,so for a few years someone had to walk in front of every car waving a red flag!This was to make sure that the car did not go too fast and hurt anyone
怎么感觉这段读起来矛盾,前面说危险,后面怎么说不快没有任何人伤亡这里的so for怎么解释!

答案

但是,在英国那时车很危险,所以很多年人们当在车前走的时候要摇红旗(警示车辆),这样保证车不会太快而撞到人.