Fact 1: Melting means changing from a solid into a liquid by adding heat energy. Fact 2: Melting is a phase change. Given the two facts above, what changes a solid into a liquid using heat energy?

Choose from: a. electricity. b. It gets heated up. c. boiling. d. aqueous solution. e. a phase change. f. a hydraulic system. g. heating liquids. h. Water expanding.
The answer is:
e.