A heading is basically the title of the letter the introduction is the reason for writing the letter the argument is the problem and the closing is a recap So your answer would be B. Introduction. I hope this helped. :)
Option B is correct since it is the introduction the right place to state the purpose of the cover letter. Candidates to occupy a post in a company usually should make reference to it and its prestige in the market. In addition, they have to explain how their skills could fit the necessities of such company. The purpose of the letter must always be brief, but also clear and direct.
