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

The brain is the most complex organ in the human body.
What is the most complex organ in the human body?

In the lungs, oxygen diffuses out of the alveoli and into capillaries.
In the lungs, oxygen diffuses out of the alveoli and into where?

Large mutations is essential for forming new genes.
What is essential for forming new genes?