Everyone had an application form in his hand,but no one knew which room (to send it to).请问括号里的部分做什么成

题目

Everyone had an application form in his hand,but no one knew which room (to send it to).请问括号里的部分做什么成分啊?另外逗号后边的整句话是什么结构?

答案

括号里的是动词不定式做定语,修饰room
后面半句的意思是：但没人知道应当把它送到哪个房间.