题干
The old couple have been married for 40 years and never once _________ with each other.
A：they had quarreled
B：they have quarreled
C：have they quarreled
D：had they quarreled
答案(点此获取答案解析）
C
4NO（g）＋6H2O（g），下列叙述中正确的是（ ）