Marine mammals, with a few exceptions, are
a. oviparous
b. ovoviviparous
c. viviparous

Marine mammals , with few exception are viviparous.

Explanation:

Mammals are those animals which are characterized by the presence of mammary gland and body hair.They feed milk to their young ones.The vertebrates are classified as viviparous, oviparous and ovoviviparous depending on the way their young ones develop and are nourished during their embryonic and foetal development.Viviparous animals are those which directly give birth to their young ones and have a distinct gestation period during which their babues develop inside their womb. These are placental mammals.Oviparous animals are those which lay egg and the embryo develops outside mothers body.Ovoviviparous  animals are those who do not lay their eggs but their eggs hatch inside their body .These are aplacental animals.Most mammals are viviparous.