how to create data validation drop-down list based on three conditions...

Here is a simple table that can explain the problem i hv....
i would like to find value of X1+Y1+Z1, but in the table there's two values with same criteria...
i would like to create drop-down list to each column A, B, C and D
A to show X values
B to show Y values
C to show Z values
and thn D show the values of combine 3 criteria...
can someone help me?

Im confused DV D have combine A, B and C? but you values member on D is 10, 12, 12, 15, 15, 15, 20, 21?

my bad, what i means is In the values of DV D is depend on A, B, and C...

im sry, this is the correct table of my problem

what i want to find is in DV A, B, C, i select X1, Y1, and Z5
in the DV D i can select the values 6,
in my task, the DV D(after choosing the X1, Y1, Z5) hv many different values