A Sensitivity label must contain at least one classification and one category set. Category set and Compartment set are synonyms, they mean the same thing. The sensitivity label must contain at least one Classification and at least one Category. It is common in some environments for a single item to belong to multiple categories. The list of all the categories to which an item belongs is called a compartment set or category set.
The following answers are incorrect:
the item’s classification. Is incorrect because you need a category set as well. the item’s category. Is incorrect because category set and classification would be both be required.
The item’s need to know. Is incorrect because there is no such thing. The need to know is indicated by the catergories the object belongs to. This is NOT the best answer.
Reference(s) used for this question: OIG CBK, Access Control (pages 186 -188) AIO, 3rd Edition, Access Control (pages 162 -163) AIO, 4th Edittion, Access Control, pp 212-214.
Wikipedia –http://en.wikipedia.org/wiki/Mandatory_Access_Control