**Core Concept**
One primary oocyte undergoes meiosis to produce a mature ovum. This process involves two successive cell divisions: meiosis I and meiosis II. During meiosis, the primary oocyte divides to produce a mature ovum and a smaller polar body, which contains most of the cytoplasm and some organelles.

**Why the Correct Answer is Right**
The correct answer is A. 1 because during meiosis I, the primary oocyte divides to form a mature ovum and a first polar body. The first polar body then undergoes meiosis II to produce a smaller second polar body and a mature ovum, which is released during ovulation. This process ensures that each mature ovum has a unique set of chromosomes, while the polar bodies have non-viable, haploid sets of chromosomes. The presence of only one primary oocyte forming one ovum is a critical aspect of the reproductive cycle.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incorrect because one primary oocyte does not divide to form two mature ova. Instead, one primary oocyte forms one mature ovum and a polar body.
**Option C:** This option is incorrect because one primary oocyte does not divide to form three mature ova. The correct division is one primary oocyte forming one mature ovum and two polar bodies.
**Option D:** This option is incorrect because one primary oocyte does not divide to form four mature ova. As mentioned earlier, the correct division is one primary oocyte forming one mature ovum and two polar bodies.

**Clinical Pearl / High-Yield Fact**
A key aspect of oogenesis is the reduction in the number of oocytes from millions to about 1-2 million at birth, which is further reduced to a few hundred thousand at puberty. This reduction in oocyte number is due to the process of atresia, in which oocytes degenerate and are resorbed by the body.

**✓ Correct Answer: A. 1**