1. This question is being asked for the third time.

-> Câu bị động hiện tại tiếp diễn: S + is/am/are + being + Vpp

2. Social network has been used for many purposes these days by teenagers.

-> Câu bị động hiện tại hoàn thành: S + have/has + been + Vpp 

3. I suggested that energy-saving appliances should be used instead of ordinary ones to save energy.

-> S1 + suggest + S2 + should + Vinf

4. If they were strong enough, they could lift the heavy door.

-> If 2: If + S1 + V2/ed, S2 + would/could + Vinf 

1 . This question is being asked you for the third time

( Bị động hiện tại tiếp diễn )

2 .  Social network has been used for many purposes these days by teenagers

( Bị động hiện tại hoàn thành )

3 . I suggested that energy-saving appliances should be used instead of ordinary ones to save energy

( suggest that sb should do sth/ sth should be done )

4 . If they were strong enough , they could lift the heavy door

( Câu đk loại 2 )