Final answer:
ICANN and Verisign are responsible for managing the top-level domain name, with ICANN overseeing the domain name system and Verisign having authority over certain domains like .com and .net.
Step-by-step explanation:
The two related organizations responsible for managing the top-level domain name are ICANN (Internet Corporation for Assigned Names and Numbers) and Verisign. ICANN is a non-profit organization that coordinates the global Internet's systems of unique identifiers and, in particular, ensures the network's stable and secure operation. Verisign, on the other hand, is a company that operates a diverse array of network infrastructure, including two of the Internet's thirteen root nameservers, and is responsible for the registry services for certain top-level domains.
Option "a" ICANN and Verisign is the correct pair. ICANN oversees the entire domain name system while Verisign has been granted the authority to manage specific top-level domains by ICANN, under contractual agreement, which includes the registry of domains such as .com and .net.