Answer:
TYPE OF LIQUID SUBSTANCE RECEIVED
Explanation:
The independent variable in an experiment is the variable that the experimenter deliberately changes or manipulates in order to bring about a response in the dependent variable/measured variable.
In this experiment, the TYPE OF LIQUID was changed for each group of plant in order to see how it affects how the plants grew. Hence, the TYPE OF LIQUID is the independent variable while the dependent variable is the plant growth, which is dependent on the independent variable.