- 'Marc Andreessen' -> 'Twitter URL' -> 'https://twitter.com/pmarca' is correct, as this is the primary and official Twitter URL for marc Andreessen as evidenced by his page on a16z.com https://a16z.com/author/marc-andreessen/.
- 'Ethereum' -> 'Twitter URL' -> 'https://twitter.com/ethereum' is correct, as this is the primary and official Twitter URL for Ethereum as evidenced by the Ethereum foundation's official community links page https://ethereum.org/en/community/online/.
- 'Marc Andreessen' -> 'Twitter URL' -> 'https://twitter.com/pmarca_blog' is incorrect, as this Twitter profile is not officially affiliated with Marc Andreessen on any external website.