—is the Changjiang river in China do you know?—Yes it’s about 6 380 kilometers long.A. H

问题补充：

—is the Changjiang river in China, do you know?

—Yes, it’s about 6,380 kilometers long.

A. How many

B. How wide

C. How long

D. How much

答案：

A. How many

B. How wide

(答案→)C. How long

D. How much

解析：How many多少个；How wide多宽；How long多长；How much多少钱。根据下文，是的，大约6380千米长。可知上文问的是长江的长度，故选C。