Answer:
Type of support surface
Nutritional supplementation
Step-by-step explanation:
Variable
This is simply an element, feature, or factor that is prone to change or be altered. There is the independent and the dependent variable.
An Independent variable
This is simply refered to as a variable that is deliberately altered or changed to observe its effect on the dependent variable. It is that variable that a researcher or a scientist alters or changes and you have control over. They are the factor being tested in an experiment.
An example is the liquid used to water each plant in an experimental studies.