III. Thay đổi chủ động thành thụ động.
  21. People used oil-lamps years ago.
$\Rightarrow$Oil-lamps .................................
  22. The boss will meet  him tomorrow in the restaurent.
$\Rightarrow$He ...........................................
  23. The old woman feeds  fowls twice a day.
$\Rightarrow$The fowls .....................................
  24. Does he often  clean the windows?
$\Rightarrow$Are ......................................?
  25. Nam will buy a new bike next week.
$\Rightarrow$A new bike .................................