According to economic theory, a nation should produce and export those items （）it gains a competitive advantage.
A、
from which
B、
for that
C、
by what
D、
about it
【正确答案】：A
【题目解析】：
根据经济理论，一个国家应该生产和出口那些可以从中获得竞争优势的商品。考察定语从句，还原语序为gains a competitive advantage from those items，故选A。
