题干
They had not known each other three days ______ they began to quarrel.
A：after
B：until
C：when
D：before
答案(点此获取答案解析）
D
They had not known each other three days ______ they began to quarrel.
A：after
B：until
C：when
D：before
2C(g)，若2 s(秒)后测得C的浓度为0.6 mol/L，现有下列几种说法：