I don't believe we've met before I must say you do look familiar.A. thereforeB. althoughC

问题补充：

I don believe weve met before,I must say you do look familiar.

A. therefore

B. although

C. since

D. for

答案：

A. therefore

(答案→)B. although

C. since

D. for

解析：考查引导词，therefore表示因此；although 表示尽管…但是…；since表示自从…；for表示为了…，句子意思“尽管我不相信我们以前见过面，但是我必须说你看上去很熟悉”，句子I don believe weve met before是个宾语从句，省略了引导词that，look系动词，后跟形容词