Given a scientific question, generate a correct answer to it.

[Q]: Studies have shown that not only does reproduction have a cost as far as how long male fruit flies live, but also fruit flies that have already mated several times have limited amounts of this?
[A]: sperm

[Q]: A turbine that spins a generator will produce?
[A]: electricity

[Q]: Which single most factor is responsible for the extinction of hundreds of species of birds?
[A]:
human actions