The following sentences contain blanks. Use the drop-down menus to complete each blank correctly. Most of the world’s nonrenewable energy sources are [Dropdown 1] . When they are burned, they create greenhouse gases that contribute to climate change. For example, most vehicles in the world are powered by an internal [Dropdown 2] that burns gasoline to produce energy. To limit damage from “dirty” energy sources, innovators have developed [Dropdown 3] sources, such as solar panels and wind turbines, to generate “clean” energy.