31, C - fossil (fossil fuels: nhiên liệu hóa thạch)

32, B - used (mệnh đề quan hệ rút gọn)

33, D - Between (Between … and …: giữa … và …)

34, A - electricity (n, điện)

35, B - public (public transportation: phương tiện công cộng)

36, D - He died in 1968 because of lung cancer.

37, D - In  Klushino

38, C - final (=eventual: cuối cùng)

39, C - He entered military fight training at the Orenburg Pilot’s School.

40, A - A carpenter 

41, B -> sitting

42, D -> frequently

43, C -> requires

44, A -> to whom 

45, D -> will they

46, B - The company rejected Bill’s offer.

47, D - He always thinks about the people that often help him.

48, A - The bag they left there was found, wasn’t it?

49, D - The children expected new clothes as Christmas gifts.

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