I'm struggling with a SUMPRODUCT

I have two worksheets (WS1 and WS2) both with the following columns:
'Material Number' (Column A) and 'Site' (Column B). They each have around
9000 rows. In WS2 there is another value, 'Group' (Column C)

If the a Material and Site combination from WS1 are found in WS2, return the
Group in WS2:Column C to Column C in WS1.

Any ideas?