refer to与look up的区别和用法expand与spread的区别和用法campaign与struggl的区别与用法

问题描述:

refer to与look up的区别和用法
expand与spread的区别和用法
campaign与struggl的区别与用法

refer to指的是参阅书籍,谈到或指的是
look up是查单词(而不是字典)
struggle“奋斗,挣扎”
campaign“人员众多的大型公众活动”