Which is the most appropriate statement?

A system may be defined as:

a. a set of objects together with relationships between these objects and their attributes connected or related to each other in such a manner as to form an entirety or whole.

b. two sets of objects together with relationships between these objects and their attributes connected or related to each other in such a manner as to form an entirety or whole.

c. a set of objects together with relationships between these objects and their attributes connected or related to each other in such a manner as to form several units.

d. a set of objects together with relationships between these objects or their attributes connected or related to each other in such a manner as to form an entirety or whole.