in 和my不是同一類的,in 是介詞或副詞,my 是物主代詞其後需跟名詞或動名詞,例如:
He came to visit my home yesterday but I was not in. 昨天他來我家了,可是我沒在家(本句中,my 後面跟了名詞home,in是副詞,放在了系動詞後面,在句中作表語)
I feel a little cold in the d you mind my closing the windows?我在教室裏感覺有點冷,你介意我把窗戶關上嗎(本句中,my後面跟了動名詞closing,in是介詞,後面跟了名詞the classroom)