Bread and butter ( ) their main food when they were liing in the small town.

Bread and butter ( ) their main food when they were liing in the small town.
A.is
B.are
C.was
D.were
Bread 和 butter 是二样东西,虽然说是拌在一起当一个整体的食物,但实际上它是二样东西,为什么要选 i s