**Core Concept**
The emergence of chloroquine-resistant Plasmodium falciparum strains necessitates the use of alternative antimalarial therapies. The treatment of choice for chloroquine-resistant malaria should effectively target the parasite's life cycle and prevent resistance development.

**Why the Correct Answer is Right**
Sulfadoxine + Pyrimethamine (Option B) is a combination antimalarial medication that targets the dihydropteroate synthase enzyme in the parasite's folate synthesis pathway. Sulfadoxine inhibits dihydropteroate synthase, while pyrimethamine acts as a competitive inhibitor of dihydrofolate reductase. This dual-action synergy effectively suppresses the parasite's replication, making it an ideal choice for treating chloroquine-resistant malaria. The long half-life of sulfadoxine and the short half-life of pyrimethamine allow for a single-dose regimen, which helps prevent resistance development.

**Why Each Wrong Option is Incorrect**
**Option A:** Mefloquine is an alternative antimalarial medication but is not the treatment of choice for chloroquine-resistant malaria due to concerns about resistance development and its efficacy in areas with high resistance levels.
**Option C:** Primaquine + Chloroquine is not an effective combination for treating chloroquine-resistant malaria, as primaquine is primarily used to target the liver stages of the parasite and is not sufficient to eliminate the blood stages.
**Option D:** Chloroquine + Pyrimethamine is not an effective combination for treating chloroquine-resistant malaria, as the chloroquine component will be ineffective against resistant strains.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the choice of antimalarial medication should be guided by local resistance patterns, parasite species, and patient-specific factors. The World Health Organization recommends the use of artemisinin-based combination therapies (ACTs) as the first-line treatment for uncomplicated falciparum malaria.

**✓ Correct Answer:** B. Sulfadoxine + Pyrimethamine