Which other name server addresses do DNS name servers hold by default, and why?

What will be an ideal response?

A DNS name server holds the addresses of one or more root servers, so that all parts of the name space can be
reached. It stores the addresses of servers storing subdomains (thus a server for qmul.ac.uk stores addresses of
servers for dcs.qmul.ac.uk). Thirdly, it is often convenient for it to store the addresses of servers storing its
parent domain (thus a server in dcs.qmul.ac.uk knows the addresses of servers storing qmul.ac.uk).