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

Negative growth rate results when birth rates fall even lower than death rates.
What results when birth rates fall even lower than death rates?

Producing sperm and secreting testosterone are the main functions of male reproductive system system.
Producing sperm and secreting testosterone are the main functions of what system?

Hydrogen is the most abundant element in the universe.

What is the most abundant element in the universe?