修改They are sitting on the armchair.这句话
问题描述：
修改They are sitting on the armchair.这句话
答
armchair是可数名词,意思是“扶手椅”.表示“坐在扶手椅上”应用介词in.故答案为：
They are sitting in the armchair.
由于主语是They,所以他们不能坐在一把扶手椅上.如果改为为：They are sitting in the armchairs.会更好.