Which of the following layers covering the secondary follicle is...

During the development of the ovarian follicle, the primary follicle matures into a secondary follicle. At this stage, the theca layer differentiates into two distinct layers: the inner theca interna and the outer theca externa.

The theca interna is a cellular, highly vascularized, and glandular layer responsible for secreting androgens.

The theca externa is the outermost layer and is composed of fibrous connective tissue containing fibroblasts and collagen. Therefore, the theca externa is the fibrous layer covering the secondary follicle.

Answer: Theca externa