Q: You are presented with the quiz "What causes thermal expansion?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "increasing heat causes thermal expansion" and "fire puts off heat". So, what's the best answer to the question?

Options are:
[1]. fear
[2]. cold
[3]. coal
[4]. energy
[5]. Sun
[6]. fire
[7]. ice
[8]. wind
The answer is:
[6].