**Core Concept**
Postmenopausal osteoporosis is a condition characterized by a decrease in bone mass and density, leading to an increased risk of fractures. The prevention of postmenopausal osteoporosis involves the use of medications that either increase bone formation or decrease bone resorption. Non-hormonal drugs are often preferred as an alternative to hormone replacement therapy (HRT) due to its associated risks.

**Why the Correct Answer is Right**
Bisphosphonates are a class of non-hormonal drugs that are commonly used to prevent postmenopausal osteoporosis. They work by inhibiting osteoclast-mediated bone resorption, thereby increasing bone density and reducing the risk of fractures. Bisphosphonates bind to hydroxyapatite in bone, which prevents osteoclasts from breaking down bone tissue. This results in a net gain in bone mass and a decrease in the risk of osteoporotic fractures.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a non-hormonal drug. Hormone replacement therapy (HRT) is a hormonal treatment that can be used to prevent postmenopausal osteoporosis, but it is not a non-hormonal option.
**Option B:** This option is incorrect as it is the correct answer. Bisphosphonates are a class of non-hormonal drugs that are commonly used to prevent postmenopausal osteoporosis.
**Option D:** This option is incorrect as it does not specify a non-hormonal drug. Selective estrogen receptor modulators (SERMs) are a class of drugs that can be used to prevent postmenopausal osteoporosis, but they are not non-hormonal.

**Clinical Pearl / High-Yield Fact**
Bisphosphonates are a class of non-hormonal drugs that are commonly used to prevent postmenopausal osteoporosis. They work by inhibiting osteoclast-mediated bone resorption, thereby increasing bone density and reducing the risk of fractures.

**Correct Answer: C. Alendronate**