What is the independent variable in the hypothesis:

“if a student studies for thirty minutes, then their grade will improve.”

a. the age of the student
b. the student’s grade
c. the type of class
d. how long the student studies for

D

Explanation: As the independent variable is the variable that is changed to see a difference in results (to compare results) we know they want to test different amounts of time to see whether 30 minutes will help their grades improve, so the independent variable is the time spent studying, hope this helped