The complete sentences are:
A) We tried.
B) Need more.
A complete sentence must have both a subject and a predicate and express a complete idea. In each of these sentences, there is a subject (We, Need) and a predicate (tried, more) that together express a complete idea.
Option C) Loving this. is not a complete sentence because it does not have a subject. The word "loving" is a present participle, which cannot function as a predicate on its own. A sentence needs a subject and a predicate to be complete.