I like these English songs and they _____ many times on the radio. [ ]

A. taught

B. have taught

C. are taught

D. have been taught

某加热炉的有效热负荷为397.48MJ/h，燃料瓦斯用量14.33Nm3/h，燃料瓦斯的低发热值为33MJ/Nm3，则加热炉的热效率是（）

A.74.05%

B.80.05%

C.84.05%

D.88.05%