//2a. Lấy ListDatabases
public string ListDatabases()
{
    // Replace the uri string with your MongoDB deployment's connection string.
    var client = new MongoClient(
        "mongodb://localhost:27017/?readPreference=primary&appname=MongoDB%20Compass&directConnection=true&ssl=false"
    );

    string re = "";

    // Lấy ListDatabases
    var dbList = client.ListDatabases().ToList();
    re += "The list of databases on this server is: ";

    //chạy vòng lặp lấy từng database
    foreach (var row in dbList)
    {
        re += row;              
    }

    return re;
}