Which of the following is the best example of a mechanistic understanding of a function?

1. We are self-aware so that we can recognize ourselves and distinguish ourselves from others.

2. The kidneys produce urine so that waste products, such as uric acid, do not build up in the blood.

3. Skeletal muscle cells contract when myosin heads attach to actin filaments and rotate, producing force.

4. Bones are strong so that they can support our body weight and protect delicate organs.