Final answer:
Applying bitter-tasting nail polish would be the best action to help Marge quit biting her nails.
Step-by-step explanation:
Based on the information from the text, the best action to help Marge quit biting her nails would be applying bitter-tasting nail polish. The bitter taste of the nail polish will act as a deterrent and discourage Marge from biting her nails.
While wearing gloves (option b) may physically prevent Marge from biting her nails, it is not a long-term solution and may not address the underlying habit.
Chewing gum (option c) as an alternative behavior to nail biting can be helpful, but it may not be as effective as bitter-tasting nail polish since it does not directly discourage nail biting.
Keeping nails trimmed and neat (option d) is a good general practice for nail care, but it may not be sufficient on its own to help Marge quit biting her nails.