Which group of animals possesses mammary glands?

In Prototheria,mammary glands are.....

Which characteristic is found exclusively in mammals?

Assertion : The duck-billed Platypus and the spiny ant-eater,both are egg-laying animals yet they are grouped under mammals.
Reason : Both of them have seven cervical vertebrae and $12$ pairs of cranial nerves.

Which of the following is an oviparous mammal?

Identify the group which includes animals all of which give birth to young ones directly.