**Core Concept**
The question is testing the knowledge of contraceptive methods suitable for commercial sex workers, who may require a highly effective and discreet form of contraception to prevent unintended pregnancies. **Intrauterine devices (IUDs)** are a popular choice due to their high efficacy, long duration of action, and minimal maintenance requirements.

**Why the Correct Answer is Right**
IUDs, specifically the copper-containing IUD (Cu-IUD), are an excellent option for commercial sex workers due to their high efficacy in preventing pregnancy, which is estimated to be around 99%. The Cu-IUD works by releasing ions that are toxic to sperm, thereby preventing fertilization. It is also a long-acting reversible contraceptive (LARC) method, which means it can be easily removed if the user decides to conceive in the future. Additionally, the Cu-IUD does not require user compliance or daily administration, making it an ideal choice for individuals who may have limited access to healthcare or may be at risk of inconsistent use of other contraceptive methods.

**Why Each Wrong Option is Incorrect**
* **Option A:** Oral contraceptives (OCs) are not the contraceptive method of choice for commercial sex workers due to the need for daily administration, which may be inconsistent in this population.
* **Option B:** Barrier methods, such as condoms, are essential for preventing sexually transmitted infections (STIs) but are not the most effective contraceptive method for preventing unintended pregnancies.
* **Option D:** Depot medroxyprogesterone acetate (DMPA) injections are a highly effective contraceptive method, but they require regular injections every 3 months, which may not be feasible for commercial sex workers with limited access to healthcare.

**Clinical Pearl / High-Yield Fact**
Commercial sex workers are at a higher risk of STIs, including HIV, and should be offered a comprehensive reproductive health package that includes STI screening, HIV testing, and condom promotion in addition to effective contraception.

**Correct Answer: C. Intrauterine devices (IUDs)**