**Core Concept**
Praziquantel is a broad-spectrum anthelmintic drug that is effective against various species of flatworms, including blood flukes, liver flukes, lung flukes, and cysticerci. Its mechanism of action involves the disruption of the flatworm's cell membrane, leading to cell death and ultimately expulsion of the parasite from the host.

**Why the Correct Answer is Right**
Praziquantel works by activating voltage-gated calcium channels in the flatworm's cell membrane, leading to an influx of calcium ions and subsequent cell death. This process is specific to flatworms and is not seen in other types of parasites, such as roundworms or tapeworms. Praziquantel is also effective against a wide range of flatworm species, including Schistosoma (blood flukes), Fasciola (liver flukes), Paragonimus (lung flukes), and Taenia (cysticerci).

**Why Each Wrong Option is Incorrect**
**Option A:** Albendazole is a broad-spectrum anthelmintic drug that is effective against a wide range of parasites, including roundworms, hookworms, and tapeworms. However, it is not effective against flatworms, making it an incorrect choice for this question.
**Option C:** Ivermectin is a broad-spectrum anthelmintic drug that is effective against a wide range of parasites, including roundworms, hookworms, and mites. However, it is not effective against flatworms, making it an incorrect choice for this question.
**Option D:** Thiabendazole is an anthelmintic drug that is effective against a wide range of parasites, including roundworms and hookworms. However, it is not effective against flatworms, making it an incorrect choice for this question.

**Clinical Pearl / High-Yield Fact**
Praziquantel is the drug of choice for treating schistosomiasis, a disease caused by infection with blood flukes of the genus Schistosoma. It is also effective against other types of flatworm infections, including fascioliasis (liver fluke infection) and paragonimiasis (lung fluke infection).

**✓ Correct Answer: B. Praziquantel**