Choice A rationale:

 Topical antibiotics.

Rationale: Topical antibiotics are primarily used for mild to moderate cases of acne vulgaris.

Severe cases typically require systemic treatments like oral antibiotics or isotretinoin.

Choice B rationale:

 Chemical peels.

Rationale: Chemical peels are not typically used as a primary treatment for severe cases of acne vulgaris.

They are more commonly employed for cosmetic purposes and may not effectively address the underlying causes of severe acne.

Choice C rationale:

 Isotretinoin.

Rationale: Isotretinoin, also known as Accutane, is a potent oral medication often reserved for severe or recalcitrant cases of acne vulgaris.

It works by reducing sebum production and has the potential to provide long-term remission of acne.

However, it comes with potential side effects and requires strict monitoring.

Choice D rationale:

 Benzoyl peroxide.

Rationale: Benzoyl peroxide is a topical medication that can be effective for mild to moderate acne but is not typically used as the primary treatment for severe cases.

Severe acne often necessitates systemic treatments like isotretinoin.