【题目】They had not known each other three days ______ they began to quarrel.
A.after
B.until
C.when
D.before

【答案】D
【解析】句意：他们认识还不到3天就开始吵架了。A. after在……之后；B. until直到；C. when当……的时候；D. before在……之前。故选D。