**Core Concept**
The question is testing the student's knowledge of sex determination and sex reversal in organisms. A natural transformer is an individual that can change its sex from male to female or vice versa without any external influence.

**Why the Correct Answer is Right**
In many species of fish, such as zebrafish and medaka, sex is determined by a complex interplay of genetic and hormonal factors. Natural transformers are individuals that can undergo sex reversal, where they change their sex from male to female or vice versa due to genetic or hormonal changes. This process is often triggered by changes in the ratio of sex hormones, such as testosterone and estrogen. In some species, natural transformers can change sex multiple times, and this process is often accompanied by changes in the development of secondary sex characteristics.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify a particular organism that is known to be a natural transformer.
* **Option B:** This option is incorrect because it is a type of cancer that affects the reproductive system, but it is not an organism that can change sex naturally.
* **Option C:** This option is incorrect because it is a type of genetic disorder that affects sex development, but it is not an organism that can change sex naturally.

**Clinical Pearl / High-Yield Fact**
It's worth noting that sex transformation is a complex process that involves multiple genetic and hormonal factors. In some species, natural transformers can change sex multiple times, and this process is often accompanied by changes in the development of secondary sex characteristics.

**Correct Answer: C. Zebrafish.