My uncle was a bus driver when he was young. → My uncle used ________________________________________________________

My uncle was a bus driver when he was young.

→ My uncle used to be a bus driver when he was young.

→ used to + V: từng là gì/ từng hay làm gì trong quá khứ, giờ không còn làm nữa.

Dịch: Chú tôi từng là tài xế xe buýt khi còn trẻ.