concatanate arrays c#

I have a form that generates 2 text files.
Each comprises a list of directories at a given location; displayed in a list box and output to text file.
Ideally I would like ONE text file, with EACH list in it. Both directories will always be the same so I can read the file and the entries will line up.
So...I have tried creating a single file and adding both arrays - and failed
I have tried creating a single array, populated with both lists - and failed.
Could anybody point me (a novice) in the right direction, please?
private void button5_Click(object sender, EventArgs e)
            //list the source
            string[] sfolders = System.IO.Directory.GetDirectories(@"R:\data\lister\", "*", System.IO.SearchOption.AllDirectories);
            foreach (string s in sfolders)

                listBox2.DataSource = sfolders;

            //list the destination
            string[] dfolders = System.IO.Directory.GetDirectories(@"C:\lister\", "*", System.IO.SearchOption.AllDirectories);
            foreach (string d in dfolders)

                listBox3.DataSource = dfolders;

            System.IO.File.WriteAllLines(@"C:\\lister\\DFolders.txt", dfolders);

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Richard TeasdaleFinancial ControllerAsked:
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Guy Hengel [angelIII / a3]Billing EngineerCommented:
you might want to create an arrayList, and add both arrays into it, and set the datasource to that arraylist

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