In an experiment to test the hypothesis that added phosphate will cause marigolds to produce more blooms, the experimenter has two groups of pots planted with marigold seeds. one group gets watered with phosphate added to the water, while the other group gets watered with no phosphate. both groups get the same amount of water and light.
which is a controlled variable in this experiment?
a. number of pots
b. amount of water
c. amount of phosphate
d. amount of blooms on a plant