Question

_________ is a staple of the south korean diet while ____________ is a staple of the u.s. diet.

Answer 1

RICE is the staple of South Korean diet while CORN is a staple of the US diet.
These preferences for food in these two countries are influenced by historical and social factors. 
Most of the food in South Korea are usually prepared from rice while in the US most of the staple food are prepared from corn.