如何通过T-SQL查找表的特定外键？

i want to bring ONE foreign key from several ones in a table. in the GUI interface in sql server if we expand the table options we can see a folder called "Keys", in this folder there is one primary key and several foreign ones. In my example i have three tables, Customer, Orders and Items. Customer has Customer_ID as primary, Items has Item_ID as primary and Orders has Order_ID as primary, foreign key Customer_nbr references customer (Customer_ID) and foreign key item_nbr references Items (Item_ID).i want to bring ONE foreign key from several on