An independent variable is a variable which change is not affected by that of another variable. By process of elimination you can take out B and C. An independent variable can also change so that takes out A. That leaves D.
The answer is, "Lithosphere plate boundaries."
Most earth quakes occur in the upper 10-12 miles of the earth crust as the result of failure on faults caused by the strains induced by plate motions.
I hope this helps!
13-13= 0, 19-13= 6, so then 0-6= -6
All of these are necessary, but what you need the most I would say is
D. Movement
Without movement, your body can stiff up, causing muscle problems which can lead to many various things.
