1.选C.动词不定式to be held 表示将要发生的事情,做后置定语修饰名词Party.且hold与party的关系是动宾关系（举办晚会hold the party).
拆分成2个简单句就成了：
Are you going to the party?The party is to be held at your house tomorrow.
变成主从复合句：
Are you going to the party （which is ) to be held at your house tomorow.
省略掉which is最后简化成题目原句形式.
2.选B.could you please ...这个句型结构的否定式为 Could you please not do sth,
e.g.Could you please not smoke in the room?你能不能不在房间里抽烟?
Could you please not bother me?你可以不来烦我吗?