Trying to make two lists alternate

Right now my code looks like this:

Module VBModule
Dim arrjoin As String
Dim arrtext(1) As String
Sub Main()

arrtext(0) = "a,b,c"
arrtext(1) = "1,2,3"

arrjoin = String.Join( ",", arrtext)

console.writeline(arrjoin)
End Sub
End Module

and the output looks like:
a,b,c,1,2,3

but I want it to look like:
a,1,b,2,c,3

anyone know how this could be done?

I'm new to this website and m not sure if I'm posting this in the right place so please bare with me.
Thank you in advance.