**Core Concept**
Finasteride is a 5-alpha-reductase inhibitor used in the treatment of benign prostatic hyperplasia (BPH) and androgenetic alopecia. It works by inhibiting the conversion of testosterone to dihydrotestosterone (DHT), a potent androgen responsible for the growth of prostate tissue and hair loss.

**Why the Correct Answer is Right**
Finasteride specifically targets the type II 5-alpha-reductase enzyme, which is predominantly found in the prostate gland and hair follicles. By blocking this enzyme, finasteride reduces the levels of DHT, leading to a decrease in prostate size and an improvement in hair growth. The reduction in DHT levels also inhibits the growth of prostate tissue, making it an effective treatment for BPH.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because finasteride does not primarily target the type I 5-alpha-reductase enzyme, which is mainly found in the liver and other tissues. While finasteride does have some activity against type I 5-alpha-reductase, its primary mechanism of action is through the inhibition of type II 5-alpha-reductase.
**Option B:** This option is incorrect because finasteride does not act by blocking the conversion of cholesterol to testosterone. Finasteride's mechanism of action is focused on the conversion of testosterone to DHT, not the production of testosterone itself.
**Option C:** This option is incorrect because finasteride does not act by blocking the androgen receptor. Finasteride's mechanism of action is through the inhibition of the 5-alpha-reductase enzyme, not the androgen receptor itself.

**Clinical Pearl / High-Yield Fact**
It's essential to note that finasteride has a long half-life, which allows for once-daily dosing. This is in contrast to other 5-alpha-reductase inhibitors, which require multiple daily doses.

**Correct Answer: C. Finasteride acts by blocking the type II 5-alpha-reductase enzyme, which is responsible for converting testosterone to dihydrotestosterone (DHT).**