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?