Explanation : (a) 'Discovery'refers to something that existed previously and came to knowledge later. Home is not a discovery. (b) Home is not a certain. It is a set up which comes into being as a result of a certain composition of various factors. (c) Home is not a new invention of anyone at any stage of development. So choice (d) is the best answer. Home is an institution just like 'marriage. Home is a reality only when its members accept certain principles.