Common mistakes
The second and third radicals are the same letter. They merge: رَدَّ: and come apart again before a consonant ending: رَدَدْتُ.
تَمَمَ → تَمَّ Past: heتَمَمَتْ → تَمَّتْ Past: sheتَمَمُوا → تَمُّوا Past: they (m.)يَتْمِمُ → يَتِمُّ Present: he