Where Do the Donors' Portraits Appear in Jan and Hubert

Where do the donors' portraits appear in Jan and Hubert van Eyck's Ghent Altarpiece?

A) in the semi-circular areas at the top of closed shutters
B) they were depicted Adam and Even on the outer wings of the opened doors
C) in the outer compartments of the lower section of the closed shutters
D) in the outer compartments of the lower section of the interior with the people before the lamb of God