How to do a 2-dimensional lookup?
 

I have a masterlist of data, which contains 3 columns (say A, B, C) and 25
rows. I need to get the value of the cell in column C only when the
corresponding cells in Column A and column B are matching.

Ex:Master List
DR AB TT
1 X1 n1
2 X2 n12
3 X3 n23
4 X4 n34
5 X5 n45
1 X2 n2
2 X3 n13
3 X4 n24
4 X5 n35
5 X1 n41
1 X3 n3
2 X4 n14
3 X5 n25
4 X1 n31
5 X2 n42
1 X4 n4
2 X5 n15
3 X1 n21
4 X2 n32
5 X3 n43
1 X5 n5
2 X1 n11
3 X2 n22
4 X3 n33
5 X4 n44

My Data List:
AB DR TT
X1 1
X1 2
X2 3
X4 3
X3 4
X2 1
X5 2

I want to fill the column TT using the master list