**Core Concept**
Osteoclast inhibition is crucial in the treatment of bone-related diseases such as osteoporosis and Paget's disease. Osteoclasts are large multinucleated cells responsible for bone resorption, a process mediated by the RANK-RANKL system, which involves the interaction between the receptor activator of NF-κB (RANK) on osteoclasts and its ligand (RANKL) on osteoblasts.

**Why the Correct Answer is Right**
Bisphosphonates, such as zoledronic acid, inhibit osteoclast activity by binding to hydroxyapatite in bone tissue. This binding leads to the inhibition of osteoclast-mediated bone resorption, resulting in a decrease in bone turnover and an increase in bone density. Bisphosphonates also induce apoptosis in osteoclasts through the inhibition of the mevalonate pathway, which is essential for the post-translational modification of proteins necessary for osteoclast function.

**Why Each Wrong Option is Incorrect**
* **Option A:** Estrogen does not directly inhibit osteoclasts, although it does play a role in regulating bone turnover by inhibiting osteoclast activity indirectly through its effects on osteoblasts.
* **Option C:** Corticosteroids can actually increase bone resorption by stimulating osteoclast activity, although they also have a catabolic effect on bone tissue.

**Clinical Pearl / High-Yield Fact**
Bisphosphonates are a cornerstone in the treatment of osteoporosis and other bone-related diseases, and their use has been associated with a significant reduction in vertebral and nonvertebral fractures.

**Correct Answer: B. Bisphosphonates**