i think you misunderstood the question. It doesn't ask about realistic results, it asks for a more suitable control experiment.
it's a control experiment so we can't use enzymes ( idk what u mean by real enzymes as amylase produced by salivary glands are still enzymes). the whole idea is to try to mimic the experiment without using the enzymes to compare how fast the rate of reaction is with/without the enzyme.
independent variable is the enzyme. but you can't magically take it out of the saliva so you would boil it instead to denature it.