متن اصلی - انگلیسی - 1. You should work at your English as much as...

1. You should work at your English as much as possible. 2. To avoid stuffiness, the air should be given a certain amount of motion. 3. The house ought to be cleaned as often as possible. 4. Air motion is necessary to change the air in the room. 5. The idea of such building materials might have been borrowed from the ancient Greeks.