Assume purchase order and vendor has N:1 relationship. How to implement this relationship? Select one: O a. We make the primary key for purchase order serve as a foreign key for vendor b. We make the primary key for vendor as a foreign key for purchase order c. We make the primary key for purchase order as a foreign key for vendor; or alternatively, we make the primary key for vendor as a foreign key for purchase order. O d. We need to create a relationship table to implement this relationship