Fact 1: Melting means changing from a solid into a liquid by adding heat energy.

Fact 2: Ice Sculptures melt away.

Given the two facts above, answer the question "What causes ice sculptures to turn to liquid? " with the following options: 
- UV rays
 - Snow
 - salt and water.
 - Heat energy
 - air cools
 - kinetic energy
 - Subzero temperatures
 - Water expanding


 

    Heat energy     