**Core Concept**
The question is testing the understanding of oocyte development in females. At birth, oocytes are in a specific stage of development that is crucial for their maturation and potential for fertilization later in life.

**Why the Correct Answer is Right**
At birth, oocytes are in the **primary oocyte stage**. This stage is characterized by the presence of a large nucleus surrounded by a layer of compact chromatin. The primary oocyte is not yet mature and is still in the process of undergoing meiotic prophase I. The primary oocyte stage is a critical period in oocyte development, as it lays the foundation for the eventual maturation of the oocyte into a mature egg.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the stage of oocyte development at birth.
* **Option B:** This option is incorrect because it is not a recognized stage of oocyte development.
* **Option D:** This option is incorrect because it is a stage of oocyte development that occurs after birth, during puberty.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that oocytes continue to develop and mature throughout a female's reproductive life, with the majority of oocytes being lost during fetal development and early childhood.

**Correct Answer:** C. Primary oocyte