-- is your cousin?--Shes fifteen years old.A. HowB. How oldC. How manyD. How much

问题补充：

-- is your cousin?

--Shes fifteen years old.

A. How

B. How old

C. How many

D. How much

答案：

A. How

B. How old

(答案→)C. How many

D. How much

解析：How怎样；How old多大；How many多少个；How much多少钱。根据下文，她十五岁。可知上文提问年龄，故选C。