which of the following conditions is necessary for natural selection to occur?

each individual organism that is born must survive.
more organisms are born than can survive.
there must be no mutations among organisms.
there must be no variation among organisms.

I believe it is the second one "more organisms are born than can survive" because natural selection, although it is not solely based on "survival of the fittest" does have to do with an ecosystem that can only maintain a certain amount of organisms, and those that are better conditioned for the ecosystem will survive. 

Sorry I cannot be more sure, I had bio quite a while ago. 

It makes up an community

Some of her  assignments would be creation of drugs. she is a medical chemist after all so she'd need to have the necessary knowledge to make medicine which can later be sold in a pharmacy