using System;

using System.Text;

using System.Collections.Generic;

public class Program

{

    static List<List<string>> input = new List<List<string>>()

    {

        new List<string>() {"a", "b", "c"},

        new List<string>() {"d", "e"},

        new List<string>() {null},

        new List<string>() {"f", "g"},

        new List<string>() {"h"}

    };

    public static void Main()

    {

        StringBuilder sb = new StringBuilder();

        List<string> priorPerm = new List<string>();

        foreach (List<string> curList in input)

        {

            if (curList[0] == null)

            {

                foreach (string perm in priorPerm)

                {

                    sb.AppendLine(perm);

                }

                priorPerm = new List<string>(); 

            }

            else if (priorPerm.Count == 0)

            {

                Console.WriteLine(1);

                priorPerm.AddRange(curList);

            }

            else

            {

                List<string> newPerm = new List<string>();

                foreach (string perm in priorPerm)

                {

                    foreach(string curStr in curList)

                    {

                        newPerm.Add(perm + " " + curStr);

                    }

                }

                priorPerm = newPerm;

            }   

        }

        // Don't lose last iteration

        foreach (string perm in priorPerm)

        {

            sb.AppendLine(perm);

        }

        Console.WriteLine(sb.ToString());

    }

}