Mary is the only one of the teachers who a little Chinese because she is one of my friend

问题补充：

Mary is the only one of the teachers who a little Chinese because she is one of my friends who been to China.

A. know；have

B. knows；has

C. knows；have

D. know；has

答案：

A. know；have

B. knows；has

(答案→)C. knows；have

D. know；has

解析：C

解析此句包含了两个定语从句，关系代词都在从句中作主语。关系代词的单复数应与定语从句的先行词的单复数保持一致。第一个从句的先行词是the only one of the teachers，指唯一的老师，从句谓

语动词应用单数形式。第二个定语从句先行词是my friends，表示的是复数概念，所以从句谓语用复数，因此答案为C项。