I could be wrong but I think the answer is D.
Hope this helps!!!
The correct way to punctuate is seen in b:
<span>To whom it may concern:
</span>
In formal settings and when you don't know the exact identity of the person a dresses it is usual to use a colon in this situation.
I believe it's B. It seems to be the only one that is very blunt and uses a different tone from the other sentences.
