The White Granite of the Idaho Batholith near Boise, Idaho

The white granite of the Idaho Batholith near Boise, Idaho, contains dark gray xenoliths of metamorphic material.Which is older? How do you know?

A) Granite; the principle of superposition
B) Xenoliths; the principle of cross-cutting relations
C) Granite; the principle of unconformities
D) Xenoliths; the principle of inclusions