What is the role of nodes in a blockchain network?

The correct choice emphasizes that nodes in a blockchain network are integral to its functionality by maintaining a copy of the blockchain and participating in transaction validation. Nodes are essentially the backbone of the network, ensuring that every participant has access to the same data, which is crucial for the decentralized nature of blockchain technology. This replication of data promotes transparency and prevents manipulation, as all nodes must agree on the state of the blockchain through consensus mechanisms.

Furthermore, participating in transaction validation means that nodes are responsible for confirming and adding new transactions to the blockchain. This process often involves solving complex cryptographic puzzles or reaching a consensus on the validity of transactions, which fortifies the network against fraudulent activities.

In contrast, the other choices do not encapsulate the primary functions of nodes. Managing server settings and user permissions pertains more to system administration rather than the core operations of blockchain technology. Serving as a primary interface for users typically involves front-end applications that interact with the blockchain rather than the nodes themselves. Developing new blockchain technologies falls outside the scope of how nodes operate within an existing network; this task is usually performed by developers and researchers who design and implement new features or improvements.