31. Water vapour and carbon dioxide happen in the air naturally.

occur = happen: xảy ra

32. One of the greatest problems in our city is pollution.

contamination = pollution: ô nhiễm

33. My father is very tired after the long walk.

exhausted = very tired: vô cùng mệt mỏi

34. When we boil water at 100 degrees celsius, water will vapourize.

change into vapour: biến thành hơi nước = vapourize: bốc hơi

35. Lead and smoke are discharged in engine exhausts as small particles.

emit = discharge: thải ra ; tiny = small: nhỏ

36. Light that is converged can burn paper easily.

bring into one tiny point: đưa về thành một điểm = converge: hội tụ

37. The authority will build some motels along the super highway.

motel: nhà nghỉ

38. The farmers can fertilize.

fertilize: bón phân

39. You can combine two sentences into one.

join together: hợp thành = combine

40. He wasted a great sum of money in one day.

waste money: lãng phí tiền bạc, tiêu tiền không hợp lý