1. 

CORRESPONDENCE

A. Agreements
B. Contracts
C. Documents
D. Letters

Answer: Option D

Explanation:

Main Entry: Correspondence

Part of Speech: noun

Definition: communication by writing

Synonyms: exchange of letters, letters, mail, messages, post, reports, writing.


Basically correspondence means the letters that are passed between correspondants. So, the answer is letters only. If 'letter' would not be present among given options then one could go for agreement.