Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: A student proposes the rate of increase in a plant's mass will be proportional to the length of light exposure per day when all other variables are constant. How should this proposal be classified?
as a hypothesis
Proportional growth model.