Common mistakes
The second and third radicals are the same letter. They merge: رَدَّ: and come apart again before a consonant ending: رَدَدْتُ.
اِهْتَمَمَ → اِهْتَمَّ Past: heاِهْتَمَمَتْ → اِهْتَمَّتْ Past: sheاِهْتَمَمُوا → اِهْتَمُّوا Past: they (m.)يَهْتَمِمُ → يَهْتَمُّ Present: he