be someone's department
US /biː ˈsʌm.wʌnz dɪˈpɑːrt.mənt/
UK /biː ˈsʌm.wʌnz dɪˈpɑːrt.mənt/

1.
是某人的職責, 是某人的專業領域
to be someone's responsibility or area of expertise
:
•
I can't help you with that; it's not my department.
我幫不了你;那不是我的職責範圍。
•
Handling customer complaints is her department.
處理客戶投訴是她的職責。