21. replacement
22. separation
23. time-summing
24. energetic
25. enormously

26.C
27.D
28.C
29.A
30.B
31.A
32.C
33.D
34.D
35.B

36.C -> Therefore
37.B -> But
38.A -> having
39.A -> excited
40.B -> have been

41.A
42.B
43.D
44.B
45.A
46.A
47.D
48.B
49.C
50.B

51.B
52.C
53.D
54.B
55.B
56.A
57.B
58.B
59.D
60.C

21. replacement
22. separation
23. consuming
24. energize
25. enormously

61. We are looking for a cheap and clean, effective source of power that doesn’t cause pollution or waste natural resources
62. At present, most of our electricity comes from the use of coal and gas, oil or nuclear power
63. This power could be provided by the sun
64. One percent of the solar energy that reaches the earth is enough to provide power for the total population
65. Many countries are already using solar energy
67. The energy can be stored for a number of days
68. On cloudy days you can use solar energy, too
69. Sweden has an advanced technology solar energy
70. Cars will use solar power instead of gas by the year 2020