When an Ad Is to Be Printed in Two Colors,sometimes

Multiple Choice

When an ad is to be printed in two colors,sometimes two separate art boards are made (one for each color) ,and sometimes the second image is glued onto a clear plastic thin sheet that lies on top of the first image.The first image is called the:

A) first cover.
B) art set-up.
C) ad foundation.
D) base art.
E) keystone art.