1.Our friends send these postcards to us
=> These postcards are sent to us.
2.Their grandmother told them this story when the visited her last week
=> This story had been told by their grandmother they visited her last week. ( có thể bỏ từ "grandmother ... last week" nha, tại anh ko chắc )
3.Tim orderred this train ticket for his mother
=> This train ticket had been orderred by Tim for his mother.
4.You didn't show me the special camaras
=> The special cameras hadn't been shown me.
5.She showed her ticket to the airline agent
=> Her ticket had been shown to the airline agent.
6.The Greens are going to paint this house and these cars for Christmas Day
=> This house and these cars are going to be painted by the Greens for Christmas Day
7.The students have discussed the pollution problems since last week
=> The pollution problems have been discussed since last week
Chúc em học tốt !