Mr.Smith as well as his students, ________ a song in English when I came in．
A.sangB.were singingC.was singingD.is singing在线课程C
解析：
此题考查主谓一致。句子的主语是Mr．Smith, as well as连接的成分不作主语，因此谓语动词要用单数，受“when I came in”从句限制，要用过去进行时。