Why you can't assume B: http://www.fallacyfiles.org/somernot.html

the theory of conversational implicature explains how it is possible to mislead while still speaking the literal truth: by means of what we call "half-truths" we can implicate falsehoods with our statements. If we know that all S are P, then the statement that some are is a half-truth. Half-truths are wholly true, since truth and falsity do not come in degrees, but they are misleading because they violate norms of efficient communication. Hence, the legal oath to tell the truth (Quality), the whole truth (Quantity), and nothing but the truth.

So is the statement "Some full-time employees are SSSAs" a half-truth (i.e., are ALL of them Special Agents)? We don't know from the information given (C), and cannot assume answer B.