either of,both of 用法怎样区分?
1.The young people planted hundreds of trees on both sides of the street.
2.He found two guys blocking his way at both ends of the lane.
3.There are trees on either side of the street.
上述三个句子可以互换吗?即either换成both来代替吗?如果不能,可否讲一下为什么?什么情况用either,什么情况要用both呢?