China is one of ____oldest countries in ____world.

问题描述:

China is one of ____oldest countries in ____world.
A:an,the
B:the ,the
C:the,a
D:an,a
为什么?什么时候用a 什么时候用the

选B *前一定要加the.in the world是固定词组也一定要加the.