He could race multiple cars with different weight added on them and do multiple races (just to be sure) and see if his theory was correct, if not he should right down what he has learned from his experience! :D
-You'll never learn if u don't try ;)
I believe that it would be that mass and texture affect the amount of friction. Hope this helps!
A is your answer I believe because they do indeed provide a way to review other scientists work and or experiments
