In Formal letter^x, Difference between^x, Formal letters^x

Which way would be more appropriate when used in a formal letter? Are both expressions correct ( I know they're both in use, though), and is there any difference between them? Thanks a lot, N.

Kooyeen wrote: I was told to use the present or past perfect in those situations, but I often find the present continuous (even in newspapers). Kim O'Donnel: This is the first time I'm hearing a negative report. He is surprised. And he says that hearing reports is happening...