What’s the possible greatest contribution made by Zhang Qian on his first expedition to the West Regions？

What’s the possible greatest contribution made by Zhang Qian on his first expedition to the West Regions？
A.Building up an alliance with Darouzi（大月氏）.
B.Bringing back reliable information about the Western Regions.
C.Introducing China to other nations.
D.Creating a tragedy for China’s history.
正确答案：Introducing China to other nations.