What is the MOST important reason to control the condition of an experiment?

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

Wich organism obtains its energy from dead or decaying matter

Which best describes a benefit of using dna technology in medicine? a) medicine can be produced in mass quantities. b) medicine can be distributed at a reduced cost. c) medicines have fewer side effects. d) medicines are resistant to antibiotics.