Read the introduction and first paragraph of an essay about energy sources.(1) The nation's energy use is largely dependent on fossil fuels. (2) These fuels are nonrenewable resources, and they cause pollution. (3) We cannot continue our reliance on a fuel that will eventually run out. (4) Thus, we must find other ways to sustain our energy demands. (5) Pursuing alternative fuel sources is the key to solving our energy crisis.(6) Currently, about 1 percent of energy in the United States is produced by the sun, and solar energy has the potential to become a more widely used energy source. (7) Through different technologies, such as solar cells, scientists have learned to use the sun’s radiation to create electricity. (8) Solar energy is both inexhaustible and clean. (9) The major limit to this alternative source is that equipment is expensive. (10) Developing a cost-effective way to harness the power of the sun will be a significant development in solving our energy crisis. Which sentence is the author's thesis statement?