Chemical? Perhaps because it is changing?
A. is definitely true. The age of the plants and the amount of caffeine are two variables. The experimenter should have used only plants of the same age in order to determine the effect of caffeine.
b. is wrong. The amount of caffeine used was a variable.
c. is wrong. Temperature, water, and light were constants.
d. is wrong. The statement is a hypothesis that the experiment is trying to prove
8 they have eight :))))))))
The best answer to your question would be B:those who could not be broken down by physical means.