Why is genetic variation within a parasite population a critical factor for the development of drug resistance?

It allows some parasites to have a pre-existing trait for survival.

It causes the drug to become less effective over time due to chemical interactions.

It ensures that all parasites will eventually be exposed and develop immunity together.

It allows parasites to intentionally alter their genetic code to fight the drug.

A new antibiotic is developed that is highly effective against a specific strain of bacteria. If a small number of these bacteria already have a random mutation that confers resistance, what is the most likely outcome after several years of the antibiotic being used?

The antibiotic will become progressively stronger over time.

The bacterial population will be completely eradicated by the antibiotic.

The antibiotic will become less effective as the resistant bacteria become dominant.

The bacteria will likely lose the resistance mutation because it is no longer needed.

The drug itself contains nutrients that boost their reproductive rate.

The drug has eliminated their non-resistant competitors for resources.

The mutation for resistance is directly linked to a gene for faster reproduction.

The parasites sense the danger and increase reproduction as a survival strategy.

The drug will need to be administered in higher doses to achieve the same effect.

The drug eventually becomes ineffective for treating the majority of infections.

The parasite population will evolve to become completely dependent on the drug for survival.

The drug will successfully eliminate the parasite population entirely from the environment.

It causes new, beneficial mutations to appear in all parasites.

It acts as a selection pressure, favoring parasites with pre-existing resistance.

It weakens the parasites' immune systems over several generations.

It equally reduces the reproductive rate of all parasites in the population.