Need a solution on dataset as given below
;with LetterSet as
(
    select *,
        row_number() over(partition by FirstCol order by SecondCol) as rownum
    from YourLettersTable
)
select
    FirstCol,
    SecondCol,
    ThirdCol,
    FourthCol,
    FifthCol
from LetterSet
where rownum = 1


Likewise, you could have rownum = 2 for your second result set.