From the given columns, which of the combinations best describe the concepts of product hierarchy?

List-I	List-II
a. Need family	1. The core need that underlines the existence of a product family
b. Product family	2. Group of items within a product line that share one of several possible forms of the product
c. Product class	3. Group of products within the product family recognised as having a certain functional coherence
d. Product line	4. All the product classes that can satisfy a core need with reasonable effectiveness