`4.`

`a)` Because the water is polluted, the fish die.

`b)` Because of the noise, she can't sleep.

`=>`Because + S + V, S + V : Bởi vì...

`=`Because of + N/Ving, S + V

`5.`

`a)` Many houses were destroyed by the typhoon yesterday.

`=>`Bị động với quá khứ đơn : S + was/were (not) + Vpp + (by O)

`b)` People trapped in collaged buildings have been freed by rescue workers.

`=>`Bị động với hiện tại hoàn thành : S + have/has (not) + been Vpp + (by O)

`6.`

`a)` After most people had left, the volcano errupted.

`b)` Before they came to give a present, Linda had left.

`=>`Before `=`By the time `=`When + S + V2/ed, S + had + Vpp

`=`After + S + had + Vpp, S + V2/ed

`*`Hành động xảy ra trước chia ở quá khứ hoàn thành, hành động xảy ra sau chia ở quá khứ đơn.