Common mistakes
The second and third radicals are the same letter. They merge: رَدَّ: and come apart again before a consonant ending: رَدَدْتُ.
رَدَدَ → رَدَّ Past: heرَدَدَتْ → رَدَّتْ Past: sheرَدَدُوا → رَدُّوا Past: they (m.)يَرْدُدُ → يَرُدُّ Present: he