Prepositional phrase related with ZAI (在) can be placed:
(a) Before subject：在香港中文大學，[CP 大家都習慣坐校車上下山]。
In CUHK, people normally take the school bus on campus.
(b) Before verb：周末大家都出去玩了，只有我一個人在家[VP吃晚飯]。
Everyone was out of town on the weekend, and I am the only one eating dinner at home.
(c) After verb：他去北京玩的時候，是[V住]在親戚家的。
He stayed at his relative's house when he went to Beijing.