您应该能够执行以下操作，以获取符合任何条件的计划以及其父对象和祖父母对象:

You should be able to do something like this to get the plans which meet whatever criteria, along with their parent and grandparent objects:

// results is an anonymous type with properties Quote, Rate, Plan
var results = from q in quotes
    from r in q.Rates
    from p in r.Plans
    where p.Id < 500 /* whatever criteria */
    select new 
    {
        Quote = q,
        Rate = r,
        Plan = p
    };