Linq to sql Joins

Question

hai I am writing Joins in Linq to entities . here i am using 3 tables . but i got error like "The type of one of the expressions in the join clause is incorrect. Type inference failed in the call to Join" 

 

Here my Code is  

 

from A in db.table1

join B in db.table2 on A.id equals B.pid

join C in db.table3 on B.id equals C.ris

where A.Bid == "7521"

select new { C.ID};