One difference between monotremes and other types of mammals is

a) monotremes are viviparous
b) monotremes do not secrete milk
c) monotremes secrete milk through well-developed nipples
d) monotremes secrete milk through pores on the surface of the mother's abdomen

d) monotremes secrete milk through pores on the surface of the mother's abdomen

Explanation:

Monotremes are a specific group of egg-laying mammals (oviparous). They do not give birth to their young ones like other mammals. Thus, other mammals are viviparous. Although monotremes lay eggs but like other mammals secrete milk through mammary gland openings in the skin. Examples of monotremes are echidna and the duck-billed platypus.

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