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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