1. Tom said that he was a student in Boston University then.
2. The Christmas card was designed before.
-> Câu bị động quá khứ đơn: S + was/were + Vpp
3. It is a food-cooking contest.
4. Football has been played all over the world.
-> Câu bị động hiện tại hoàn thành: S + have/has + been + Vpp