You are presented with the quiz "what causes an object to lose energy?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "friction causes an object to lose energy" and "friction occurs when surfaces rub together". So, what's the best answer to the question?

Pick your answer from: (1). high temperature; (2). electron transport; (3). degrees celcius; (4). surfaces rubbing together; (5). heat is produced; (6). degrees Celsius; (7). depress neuronal excitability; (8). a tree falling;
The answer is:
(4).