Choose the, word or phrase (A, B, C or D) that best fits the blank space in the following passage

 

Are you looking for a cheap, clean, effective (7)_________ of power that doesn’t cause pollution or waste natural resources? Look no further than solar energy (8)_________ our Sun. 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 (9) _________ population. Many countries are already using solar energy. Solar panels are placed on the roofs of a house and the Sun’s energy is used (10) _________ water. The energy can be stored for a number of days; so on (11)_________ days you can use solar energy, too.

Are you looking for a cheap, clean, effective (7)_________ of power that doesn’t cause pollution or waste natural resources