Oxygen is the answer for this question.
Answer:
Did alleles for drug resistance occur in bacterial populations that afflict humans, prior to the widespread use of antibiotics in medicine and agriculture? a. No—mutations for drug resistance occur in response to antibiotic use. ... Yes—alleles for resistance arise due to random mutation, so are always present.
Explanation:
Over time, as oxygen levels decrease, CO2 levels increase. Respiration is correct as it uses oxygen as a reactant and releases CO2 as a byproduct.
