Choices: 1). UV rays 2). Snow 3). salt and water. 4). Heat energy 5). air cools 6). kinetic energy 7). Subzero temperatures 8). Water expanding

You are presented with the quiz "What causes ice sculptures to turn to liquid? " But you don't know the answer, so you turn to your teacher to ask for hints. He says that "melting means changing from a solid into a liquid by adding heat energy" and "ice Sculptures melt away". So, what's the best answer to the question?
Answer:
4).