A scientist designed an experiment to test the effect of temperature on bacterial growth. He grew three different cultures of the bacterium E. coli under three heat lamps at different temperatures. What was the independent variable in this experiment?

I guess A

The independent variable in this experiment is the temperature.

The independent variable in this experiment is the temperature. The scientist intentionally manipulated and varied the temperature levels in order to observe the effect it has on bacterial growth. Therefore, the temperature is the independent variable because it is changing and being controlled by the scientist.

other things being equal, I'd say the temperature.