A pesticide is sprayed on orange trees to kill fruit flies. Most of the fruit flies die, but a few survive. The survivors have genes that protect them from the pesticide. What is most likely to happen in the future?

a
There will be more pesticide-resistant fruit flies.
b
The frequency of pesticide resistant genes will not change.
c
The fruit flies will soon become extinct.
d
The fruit fly population will evolve a thicker exoskeleton.