Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Input: Consider Input: Oil is the most commonly used source of energy in the world.

Output: What is the most commonly used source of energy in the world?


Input: Consider Input: Competive exclusion princple explains why two different species cannot occupy the same niche in the same place for very long.

Output: What explains why two different species cannot occupy the same niche in the same place for very long?


Input: Consider Input: Cardiac muscle kind of muscle cells undergo twitch-type contractions with long refractory periods followed by brief relaxation periods, allowing the heart to fill with blood for the next cycle.


Output: What kind of muscle cells undergo twitch-type contractions with long refractory periods followed by brief relaxation periods, allowing the heart to fill with blood for the next cycle?