Whales are warm-blooded animals that live in cold seas. Which part of their body helps them maintain their body temperature?

Which of the following represents a correct grouping of aquatic animals?

Jaw suspension characteristic of mammals is

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.

Note the following:
$I.$ Dentition is heterodont.
$II.$ Canines are poorly developed.
$III.$ Incisors are chisel-like,poorly developed.
$IV.$ Herbivorous and diastema is present.
$V.$ The dental formula is $I \frac{2}{1}, C \frac{0}{0}, P m \frac{3}{2}, M \frac{3}{3}$.
Which of the above are true for $Oryctolagus$?

Mammals that give birth to relatively undeveloped young and raise them in a pouch are called ....