Members of which of the following groups have three ossicles in their middle ear?

Which pair of characters are found without exception in all mammals?

$A$: The duck-billed platypus and the spiny ant-eater,both are egg-laying animals yet are grouped under mammals.
$R$: Both of them have seven cervical vertebrae and mammary glands without teats.

Which group of mammals has functional mammary glands in both males and females?

Which of the following mammals have a cloaca?

Which of the following is $NOT$ a characteristic feature of the class $Mammalia$?