In the Context of Drafting a Legal Letter of Demand

In the context of drafting a legal letter of demand, the 'subject line' is:

A) The first paragraph to the letter that briefly sets out the background to the problem.
B) The substance of the demand, usually set out in the second paragraph.
C) A line of text that appears alone at the beginning of the letter and after the salutation that identifies the subject matter of the letter.
D) A polite warning at the end of the letter summarising the subject of the complaint.