the differnt ways in which the word is used in sentences句中的第一个in是啥成分，为何要加啊，应怎么

它是后面定语从句的一部分，in which……是the different ways的定语从句，in which the word is used in sentences这个句子恢复原顺序的话应该是the word is used in …… ways in sentences，加in是因为把定语从句的介词结构提前了。