Answer:
The correct answer is the kind of music each plant listens to.
Step-by-step explanation:
A variable refers to any condition or element whose value gets modifies in an experiment. A variable can take place in distinct quantities or types, and three kinds of variable, that is, dependent, independent, and controlled can be witnessed in an experiment. In the experiment mentioned, the kind of music each plant is listening to is the variable.
It is an independent variable whose value is modifying as it prevails in distinct kinds and it is the one that the student is using to witness its effect on the growth of the plant. In the experiment, this variable that differs also generate distinct effects or outcomes.