We can see that the research question that is most effective is: D. What are fossil fuels?
<h3>What is research question?</h3>
Researchquestionis actually known to be a question which is asked by a researcher which forms the basis for his evaluation, examination, and experimentation. Every good research question must be clear and focused.
We see that the selected answer is actually clear and focused and covers other aspect of the research.
