From the available data in the graph, the only variable that is not a control variable is the amount of water supplied to the plants.
Control variables
Control variables in experiments are variables that are kept relatively constant across all experimental groups.
Control variables are as opposed to experimental variables. These are variables that are manipulated across various experimental groups.
In the graph, variables such as light, type of plant, and fertilizer were kept constant across all groups. whereas, the amount of water supplied was varied. Hence, water is not considered a control variable.
More on control variables can be found here: https://brainly.com/question/17555102
