Answer: (D) Introduction
Step-by-step explanation:
The first paragraph or the part of the business letter should start with the proper introduction. The primary section of the formal business letters ought to incorporate a prologue to the reason for the business letter. It is very common way to initially thank somebody or to present yourself.
We should always give some introduction about the topic in the first paragraph and then, include salutation, message and the conclusion. Therefore, Option (D) is correct.