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.
