## Core Concept
The question revolves around a side effect of a drug used in acne treatment, specifically pigmentation changes. Acne treatment often involves medications that can have various side effects, including dermatological changes.

## Why the Correct Answer is Right
Minocycline, a tetracycline antibiotic, is commonly used for acne treatment. One of its known side effects is pigmentation, which can occur in various tissues, including the skin. This pigmentation can be a result of long-term use, which aligns with the scenario of a 17-year-old girl taking the drug for 2 years.

## Why Each Wrong Option is Incorrect
- **Option A:** While certain contraceptives can have dermatological side effects, they are less commonly associated directly with pigmentation as a primary side effect in the context of acne treatment.
- **Option B:** This option is not specified, but if assuming another antibiotic, it's less likely to be directly associated with pigmentation as a notable side effect compared to minocycline.
- **Option C:** This option is also not specified, but similar to option B, without a clear reference, it's hard to directly refute, though minocycline is a well-known cause.
- **Option D:** If assuming another acne medication, drugs like isotretinoin have various side effects, but pigmentation is less commonly highlighted as a direct side effect compared to minocycline.

## Clinical Pearl / High-Yield Fact
Minocycline-induced pigmentation is a notable side effect that can occur with long-term use. It's essential for clinicians to monitor patients on long-term minocycline for signs of pigmentation and to consider this side effect when prescribing.

## Correct Answer: B. Minocycline.