In Your Experiment in #9, If the Plant(s) Treated with Fertilizer

In your experiment in #9, if the plant(s) treated with fertilizer grew faster, would that prove plants grow faster with fertilizer?

A) Yes. Clearly that is the case.
B) No. It would support the hypothesis for that one plant type.
C) Yes. But you would have to then test whether that is true for other plants.
D) No. There's no way to know if the fertilizer was making the difference.
E) Yes. Obviously everyone should use fertilizers when they grow this one type of plant.