Which of the following mammals lays eggs?

1. A

   Hedgehog

   Hedgehog claims to be an egg-laying mammal, but it belongs to the placental group and gives birth to live young.

2. B

   Loris

   Loris claims to be an egg-laying mammal, but it is a placental primate and produces live offspring.

3. C

   Echidna

   Echidna claims to be an egg-laying mammal, and this is the key because it is one of the rare monotremes, alongside the platypus, that lay eggs instead of giving birth to live young.

4. D

   Kangaroo

   Kangaroo claims to be an egg-laying mammal, but it is a marsupial that gives birth to underdeveloped young which mature in a pouch.

Summary. Official key is (c) Echidna. Mammals are generally viviparous, meaning they give birth to live young, with the notable exception of monotremes. The echidna and the platypus are the only surviving egg-laying mammals, known scientifically as monotremes. Other options like hedgehogs, loris, and kangaroos give birth to live young or underdeveloped offspring. Therefore, option (c) is the correct answer.