Which statement does not correctly describe a theory? a. it is directly testable. b. it can be used to make predictions. c. it can be modified as new discoveries are made. d. it is based on scientific evidence.

Hydroelectricity provides about 7 percent of the electricity generated in the united states. (a) explain how a hydroelectric power plant converts energy stored in water into electricity. (b) identify two factors that determine the amount of electricity that can be generated by an individual hydroelectricity power plant. (c) describe the two main types of land-based hydroelectric power plants. (d) describe two economic advantages and two environmental disadvantages of hydroelectricity.