challenging query

Consider the following table:

A    B    C    D    select?
-------------------------------
1    FOO    A1    100    n
1    BAR    Z2    100    n
2    FOO    A1    101    y
2    BAR    Z2    101    y
3    FOO    A1    102    y
4    BAR    Z2    99    y
5    FOO    A1    99    n
6    BAR    Z2    98    n
7    FOO    AB    103    y
7    BAR    ZY    103    y

This table has the idea of "groups", that is, a group is defined as
all of the words from B that have the same number A.  The values in
column C also matter- we want to select both groups A=7 and A=1 since
they contain different values C.  Note that the groups defined by A=1
and A=3 are distinct- they do not contain the same number of words
from B, so we want to select them both.  Also note that D is datetime,
and all the rows with the same number A will have the same D (this is
actually ensured by a single row in another table.)

I want to select all of the numbers A which define distinct groups and
have the highest datetime D.  Is this possible in a SQL query?