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Graafian follicles are formed from
(a)Stroma of ovaries
(b)Columnar epithelium of testes
(c)Germinal epithelium of ovaries
(d)Assembly of ribosomes in bacteria

Answer
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Hint: The surface epithelium of ovaries consists of simple squamous-to-cuboidal epithelial cells covering the ovary. This component of the ovary also gives rise to the Graafian follicle.

Complete answer:
Some cells of the germinal epithelium of the ovary differentiate into large cells that have a prominent nucleus and divide mitotically to produce undifferentiated egg mother cells or oogonia during the fetal development.
Eventually, oogonia become larger and divide to produce a round mass of egg nest that has a cluster of many diploid cells.
One of the cells serves as the primary oocyte, while the rest form follicle cells. The primary oocyte starts first meiotic division during the follicular prenatal phase but is transitionally suspended into the prophase stage of meiosis I and is stored in the follicle.
The primary oocyte along with all the surrounding follicle cells transforms into a primary follicle, which is differentiated into secondary and then Graafian follicle. Thus, the progenitor of the Graafian follicle is the germinal epithelium cells.

Additional information:
The Graafian follicle is the stage before ovulation and after the first meiotic division has completed. The oocyte is now a haploid. The Graafian follicle is characterized by a large follicular antrum that makes up most of the follicles. Generally after the first meiotic division, the eccentrically located secondary oocyte gets surrounded by the zona pellucida and a layer of several cells known as the corona radiata. The ovum then released from the Graafian follicle into the oviduct will have three main structures: oocyte, zona pellucida, and corona radiata.
So, the correct answer is option (C) the germinal epithelium of the ovaries.

Note: The human ovary consists of two main parts: an inner medulla and outer cortex with indistinct boundaries. The medulla mainly contains the blood vessels and nerves, while the cortex is occupied by developing follicles. Various stages of the development of follicles can be seen in the cross-section of an ovary.