Two boys are playing football.(对Two boys划线部分提问）用who 后面是is 还是

状况不明,视为单数,当疑问代词who、what、which等作主语的时候,谓语动词用第三人称单数形式,如：
Who is playing football?
What makes you laugh so?
Which hat belongs to the witch?
所以who后面应该用单数的is。希望我能帮助你解疑释惑。