If you are testing how the amount of sleep students get affects test performance, what should you change in the experiment? a. the grading of the test b. which teacher each student has c. how much sleep each student gets d. how many questions are on the test

C. How much sleep each student gets

It says directly that you are trying to test how the amount of sleep a student gets affects their performance. If that is the case, it would make sense to change the hours or amount of sleep each student gets before taking the test.

diagram is missing, but i will try to explain your doubt.

answer:

amplitude is the maximum displacement or distance moved on a point of a vibrating body or wave measured from its equilibrium position.it is equal to half the length of vibration path.