**Core Concept**
The treatment of choice for postmenopausal osteoporosis involves medications that either mimic or inhibit the effects of parathyroid hormone (PTH) on bone metabolism. Bisphosphonates, such as alendronate, are a class of drugs that inhibit osteoclast-mediated bone resorption, thereby reducing bone turnover and increasing bone density.

**Why the Correct Answer is Right**
Alendronate, a bisphosphonate, works by binding to hydroxyapatite in bone, thereby inhibiting osteoclast-mediated bone resorption. This results in a decrease in bone turnover, which is characterized by a decrease in the rate of bone resorption and an increase in the rate of bone formation. Alendronate is specifically indicated for the treatment and prevention of postmenopausal osteoporosis, and it has been shown to increase bone mineral density and reduce the risk of vertebral and non-vertebral fractures.

**Why Each Wrong Option is Incorrect**
**Option A:** Raloxifene is a selective estrogen receptor modulator (SERM) that is used to prevent and treat osteoporosis in postmenopausal women. However, it is not the treatment of choice for postmenopausal osteoporosis and is not as potent as bisphosphonates like alendronate in increasing bone mineral density.

**Option B:** Tamoxifene, a SERM, is primarily used in the treatment and prevention of breast cancer. It has some effects on bone metabolism, but it is not indicated for the treatment of postmenopausal osteoporosis.

**Option C:** Estrogen replacement therapy is a treatment option for postmenopausal osteoporosis, but it is not the preferred treatment due to the risks associated with estrogen therapy, such as endometrial cancer and thromboembolic events.

**Clinical Pearl / High-Yield Fact**
Bisphosphonates like alendronate are preferred over estrogen replacement therapy for the treatment of postmenopausal osteoporosis because they have a more favorable safety profile and can be administered orally.

**✓ Correct Answer: D. Alendronate**