Explanation:

OmniScript repeat blocks expect an array under the block’s API name—in this case blkContacts—with each object containing fields whose API names match the element names (ContactPhone and ContactName). Option C correctly provides:

{
"blkContacts":[
{ "ContactPhone":"(212) 169-1475","ContactName":"Edward Stanos" },
{ "ContactPhone":"(212) 189-8979","ContactName":"Leanne Tomlin" }
],
"AccountPhone":"222154650",
"AccountName":"Acme"
}

This structure ensures the StepAccount JSON has the account fields at the root and a blkContacts array for the repeat block, causing all six values to render as designed.