We're trying to test the amount of bleach that has an effect on the stain so that is the altered variable.
The 2nd option uses different amounts of bleach to clean the same amount of stain.
If you choose the other options, people can argue that the bigger stain would be harder to clean with one cup of bleach, whereas the small stain gets two cups or the other way around.
It's not an effective way to see if the amount of bleach has an effect on stain removal.
