Their mother ________ dinner at the kitchen when a quarrel ________ among the children.[ ]

A. was preparing；was broken out

B. prepared；was broken out

C. was preparing；broke out

D. prepared；broke out

1kg煤完全燃烧时所放出的热量称为（）

A.煤的发热量

B.煤耗

C.标煤耗

D.低位发热量