**Core Concept**
The hydatid cyst of the liver is a parasitic infection caused by *Echinococcus granulosus*. Effective medical treatment aims to reduce cyst size, alleviate symptoms, and prevent complications.

**Why the Correct Answer is Right**
Albendazole is the first-line medical treatment for hydatid cysts due to its broad-spectrum antiparasitic activity against *E. granulosus*. It works by inhibiting the parasite's microtubule function, leading to the disruption of its metabolism and ultimately, its death. This is achieved through the inhibition of tubulin polymerization by binding to the colchicine-binding site.

**Why Each Wrong Option is Incorrect**
* **Option A:** Praziquantel is another antiparasitic drug but is not the drug of choice for hydatid cysts of the liver. It is more commonly used for treating schistosomiasis and other flatworm infections.
* **Option B:** Ivermectin has a broad-spectrum antiparasitic activity but is not effective against *E. granulosus*. It is primarily used for treating infections caused by *Onchocerca volvulus*, *Strongyloides stercoralis*, and other nematodes.
* **Option D:** Mebendazole is an antiparasitic drug but has limited efficacy against *E. granulosus*. It is more commonly used for treating hookworm and other nematode infections.

**Clinical Pearl / High-Yield Fact**
When treating hydatid cysts with albendazole, it is essential to administer the drug in combination with a corticosteroid to prevent the release of antigens from the dying parasites, which can lead to an allergic reaction.

**Correct Answer: D. Mebendazole.**