(C) It is divinely approved
The distinction between (B) and (C) is that (B) deals with the act of approval on the part of the gods and (C) deals with the state of the deed as being approved of by the gods. Socrates' earlier point, about something being approved because it gets approved and not vice versa, is meant to point out that we would have (C) only because of (B), and not the other way around. That is, a deed is in the state of being approved of by the gods because the gods decided to approve of it. The reverse, that the gods decide to approve of a deed because it is a deed they approve of, is nonsensical.
The three claims Euthyphro is committed to are:
(i) Something gets approved by the gods because it is holy
(ii) Something is approved of by the gods because it gets approved of by the gods
(iii) What is holy is what is approved of by the gods