单选题
They had talked only for a few minute ______ they found they were of
different opinions.
A. unless
B. while
C. before
D. once
【正确答案】
C
【答案解析】[解析] 本题考查连词．unless意为“除非”，引导条件状语从句；while引导时间状语从句，主句常用进行时：before引导时间状语从句，意为“在……前”；once引导时间状语从句，意为“一旦”，所以C项为正确答案。
[参考例句]
They had not known each other long before they got married.(他俩认识不久就结婚了。)