Question

Milk glands are found in
A. All vertebrates
B. All mammals
C. All placental mammals
D. All prototherian

Answer 1

Hint: Mammals have two mammary glands that produce milk after childbirth. The milk contains nutrients that nourish the baby. Certain hormones play an important role in the development of these glands.

Complete step by step answer: Mammals are the most dominant and successful due to well-developed brain and learnt behaviour. They are found in a variety of habitats such as polar ice caps, deserts, mountains, forests, grasslands and dark caves. Some of them adapted to fly or live in water. The body is covered by hair and is air-breathing, warm-blooded, viviparous and tetrapod vertebrates.
They have two pairs of pentadactyl limbs, each with five or fewer digits that are adapted for walking, running, climbing, burrowing, swimming or flying. Hind limbs absent in certain mammals like a whale.
Exoskeleton includes horny, epidermal hairs, spines, scales, claws, nails, hoofs, bony dermal plates. Skin is glandular containing sweat and sebaceous glands. The most unique mammalian character is the presence of mammary glands with teats producing milk for suckling the young. In humans, mammary glands are organised in structures called breasts. Breasts have alveoli that are surrounded by milk-secreting cuboidal cells; these cells drain the milk into the nipple.
So, the correct answer is option B. All mammals.

Note: Mammals are most adapted amongst the vertebrates because of Intrauterine development of foetus for its complete safety. The presence of sweat glands in mammals help to bring down the body temperature if the external temperature is high. Mammals have maximum development of brain and modifications of limbs.