Final answer:
The hair matrix contains a layer of basal cells, which are vital for hair growth and the production of new hair shafts.
Step-by-step explanation:
The hair matrix plays a fundamental role in hair growth and is found deep within the hair follicle. The correct answer to the question is d) a layer of basal cells. The hair matrix is a rapidly dividing layer of cells located just above the papilla, at the base of the hair follicle. These basal cells are responsible for producing new hair shafts as well as for the growth of the hair strand. The matrix is rich in keratinocytes that contribute to the formation of the hair. None of the other options provided (hair follicle, hair shaft, glassy membrane) contain the matrix; rather, they are structures associated with or produced by the matrix.