I need to alternate content in Column A2, A3 etc with those in B2, B3, etc Please see attached sample.

Note: Column A and B will be going down to 2000 rows, and so formula in Col D will need to go down to 4000+ with a simple copy and paste down.

This does not seem to work:
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https://www.excelforum.com/sho....wthread.php?t=142365