Riding a bicycle can be fun. But _______ you ride a bike to work, and then there isn’t one to ride home?
31. ________was difficult to save the places and buildings _____destroying their old beauty.
30. If we had followed his suggestion, we could have done the work better with _______money and ______people.
29. I won’t listen to the new CD unless I ______my homework.
28. Think after you read ____.
27. Great changes _______in our city in the past twenty years.