who引导什么从句？

who引导什么从句？he stretched the models' neck a bit ,but there was no doubt who posed for the portrait中的who 引导什么从句？

主语从句，看是什么从句，就看他所处的位置是起什么作用；
关系代词who和that的选择   关系代词who和that都可以指人，有时使用场合有区别。  （一）关系代词who的使用场合   1．who可以代表人、人格化了的动物、神话故事中的人物或有生命的事物。如：  1）The dog who is barking is our pet．（正在叫的那条狗是我们的宠物）  2）Those who want to go please sign their names here．（想去的人在此签名）  2．在从句中，作主语倾向于用who。如：   1）The girl who dances beautifully gave us a performance that day．  2）Do you know the person who spoke just now？   3．当先行词泛指代词he，they或指示代词those等时，常用who。如：  1）He who does no work gets no pay．(不劳动者不得食）   2）We are badly （非常地）in need of those who can work in real earnest． （我们迫切需要能认真工作的人）  4．先行词前出现不定冠词时，多用 who。如：  1）I have found a man who can do this work．   5．在there be
句型中，既作主语又表示人时多用who，或省略。如：  1）There is someone outside the office who wants to see you．  2）There's a m an who lives in that village．   6．不定代词one，ones，anyone等作先行词时，多用who。如：  One who works without complain is welcome here．   7．定语从句和先行词分隔，用that可能引起歧义时，应用who。如：  I saw a man in the street who was surrounded by many people．  这个句子如用that，就可能被人认为是定语从句修饰street。