**Core Concept**
Centchroman is a non-steroidal oral contraceptive that functions as an anti-estrogen and anti-progestin. It affects the endometrium and ovulation, making it an effective form of birth control.

**Why the Correct Answer is Right**
Since the question is incomplete, a general explanation of centchroman is provided. Centchroman's mechanism involves altering the endometrial environment, making it unfavorable for implantation, and possibly inhibiting ovulation in some cases.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific details of option A, it's challenging to provide a precise explanation.
**Option B:** Similarly, option B's details are not provided.
**Option C:** Option C's information is also missing.
**Option D:** Option D's details are not available for analysis.

**Clinical Pearl / High-Yield Fact**
Centchroman is known for its unique non-hormonal composition and is used in some countries as a contraceptive pill. Its non-steroidal nature makes it different from traditional hormonal contraceptives.

**Correct Answer:** D. Centchroman is an estrogen.