<；>；>；=
锅炉房储存了t天用的煤m吨，要使储存的煤比预定的多用d天，每天应该节约煤（ ）吨。
The old couple have been married for 40 years and never once ________ with each other.
A．they had quarrelled
B．they have quarrelled
C．have they quarrelled
D．had they quarreled
