Are you looking for a cheap, clean, effective source of power that doesn’t cause pollution or waste natural resources? Look no further than solar energy from the (17) ________. At present, most of our electricity comes from the use of coal, gas, oil (18) _________ nuclear power. This power could be provided by the Sun. One percent of the solar energy that reaches the Earth is enough to provide power for the total (19) ________. Many countries are already using solar energy. Solar panels are placed (20) ________ the roof of a house and the Sun’s energy is used to heat water.

50.     A. Moon               B. Sun                  C. Earth                          D. Mars

51.     A. or                     B. but                             C. so                     D. although

52.     A. popular                      B. population                   C. world              D. Vietnam

53.     A. on                              B. in                     C. of                               D. to