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

Oil is the most commonly used source of energy in the world.
What is the most commonly used source of energy in the world?

In prokaryotes, a(n) genome is composed of a single, double-stranded dna molecule in the form of a loop or circle.
In prokaryotes, what is composed of a single, double-stranded dna molecule in the form of a loop or circle?

While spermatogenesis produces four haploid sperm cells, oogenesis produces one mature ovum.

While spermatogenesis produces four haploid sperm cells, oogenesis produces one mature what?