[文法] in which

[tcvb (tcvb)]

第一次發文，懇請大家協助解答~
以下是BBC某篇新聞的節錄，想知道的是"in which..."
這邊的in是跟哪個字相關呢？

Crownstone is promoting a system in which a home's lights and
plug sockets automatically react to a resident's presence
based on them having a Bluetooth-broadcasting wearable or smartphone on them,
rather than waiting to be given a command.

感謝~

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推 trml: in this systen
→ tcvb: 感謝!