Final answer:
The apocrine gland is responsible for secreting sweat into the hair follicle, mainly found in areas like armpits and genital regions. Unlike eccrine glands that release a watery sweat, apocrine sweat is thicker and can lead to body odor due to bacterial decomposition. Thus, the option A is the correct answer.
Step-by-step explanation:
The gland that secretes sweat into the hair follicle is the apocrine gland. Apocrine glands are associated with hair follicles in areas such as armpits and the genital region, and are typically larger than eccrine glands. These glands secrete a sweat that includes not only water and salts but also organic compounds that make it thicker. This type of sweat is subject to bacterial decomposition, which can result in body odor. In contrast, eccrine glands secrete a more watery sweat and are not typically associated with hair follicles; they open directly on the skin surface. Moreover, sebaceous glands produce an oily substance called sebum, not sweat, which is secreted into hair follicles to help waterproof and moisturize the hair and skin.