1、当 "which" 用作关系代词时。通常会被介词如"in","on","at","by","with"等所预置。使用的介词取决于上下文和 "which" 之前的动词。
2、介词+which，怎么确定介词的举例："on"+which是用于指正在工作的书："The book on which I am working is very interesting." (我正在工作的那本书很有趣)"in"+which用于指说话者出生的城市："The city in which I was born is very beautiful." (我出生的那个城市非常美丽)"with"+which用于指说话者去参加聚会的人："The person with whom I am going to the party is my best friend." (我和谁去参加聚会是我最好的朋友)