To code a many$-$to$-$many relationship between products and customers, you add a navigation property to the Product class that$$s a collection of $\_\_\_\_\_\_\_\_\_\_\_\_$ objects and a navigation property to the Customer class that$$s a collection of $\_\_\_\_\_\_\_\_\_\_\_\_$ objects.

a$.$

Customer $-$ Product

b$.$

Customer $-$ Customer

c$.$

Product $-$ Customer

d$.$

Product $-$ Product