What has happened to the father in full fathom five
(a, he has turned into a sea creature)
(b, he has been diving to explore the sea)
(c, his body has been turned into riches of the ocean)
(d, he has lost his children at sea

The correct answer is C) his body has been turned into riches of the ocean.

In “Full Fathom Five”, the father drowned, so that is why his body has been turned into riches of the ocean.

The poem mentioned this way: “Full Fathom Five thy father lies; of his bones are coral made; Those are pearls that were his eyes; Nothing of him that doth fade; But doth suffer a sea change; Into something rich and strange.”  

The poem “Full Fathom Five” was written by Shakespeare as part of “The Tempest”, Act 1, scene II. That part of the poem refers to a shipwreck due to a storm in the sea, where the father drowns.