PLEASE HELP! Read the scenario. A biologist sets up an experiment to see how different antibiotics
affect the growth of the bacteria Clostridium perfringens. She
grows colonies of the bacteria on four different Petri dishes filled
with agar, a growth medium containing nutrients for the bacteria.
She then applies a different antibiotic to three of the bacteria
colonies in the Petri dishes. She leaves the fourth Petri dish to
grow bacteria without any antibiotic.
size of the Petri dish, nutrient agar, diameter of the
bacteria colony Each Petri dish is the same size, contains the same nutrient agar,
and is placed in an incubation chamber at the same temperature.
At the end of the experiment, the biologist measures the diameter
of the bacteria colonies on the Petri dishes.

Question: What factors must be kept constant in the experiment to obtain
valid results?

A. type of antibiotic, nutrient agar, temperature

B. nutrient agar, temperature, bacteria species

C. bacteria species, type of antibiotic, diameter of the
bacteria colony

D. size of the Petri dish, nutrient agar, diameter of the bacteria colony