Answer:
Fertilizer
Step-by-step explanation:
The student wants to measure the affect of fertilizer on the growth rate of grass seeds.
Thus, fertilizer here is an independent variable while growth of grass seeds is a dependent variable
An independent variable is the one whose impact is studied on the dependent variable while a dependent factor is the one which is impacted by the variations in the independent variable.
All other factors such as type of soil , water and sunlight remains the same.