hard for me to choose..

Rice is the ____ food for Southeast Asians.

A. common

B.general

C.staple

D.popular

I think these options are all OK, but C might be the best, the others couldn't be regarded as wrong answers.

i thought it was D

maybe D ..

C. Staple means it is a necessity. All would work properly but only staple fits the sentence perfectly, both grammatically and factually. Rice isn't just common or general or popular, it is a staple part of the diet in Southeast Asia and many other parts of the world. 

thanks a lot!