LINQ DBML不允许我从任何表插入，更新，删除或选择数据？为什么？

I've created a DBML file for a LINQ to SQL mapping and after dragging all of my tables into the designer surface. In the properties of each table, the "Delete", "Insert" and "Update" are grayed out so they're not editable like they're disabled. I'm not sure why this is. Does anyone know how to make it so that I can insert, update and delete the values inside of those tables?I've created a DBML file for a LINQ to SQL mapp