ASP.NET C＃部分类在单独的文件中不工作CS1061

I have an asp.net page called prequal.aspx with a codebehind of prequal.aspx.cs. It works. I want to separate out each client code from this page into their own partial files (to reduce chance of modifying the wrong one by mistake later.) Both .cs files begin as such:I have an asp.net page called prequal.aspx with