Answer the following question: You are presented with the quiz "What part of a car easily changes shape from smooth to compacted by physical force?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "crumple means change shape from smooth into compacted by physical force" and "crumple zones and bumpers are often weaker and poorer performing than in cars". So, what's the best answer to the question?

Available choices:
1). rock;
2). arteries;
3). fender-bender;
4). an object;
5). bumper;
6). wreck;
7). Gravity;
8). sedan;
Answer:
5).