In a distributed database implementation, it is common to have more than one main database to ensure data redundancy and enhance fault tolerance. Therefore, the configuration with both multiple main databases and multiple servers to handle applications and other tasks is a valid distributed system. The best options are those that include at least two main databases and one application server to manage the connections. Among the provided options, the configuration with 1 application server, 2 main DBs, and 1 node server is a valid distributed database implementation.