Common mistakes
The second and third radicals are the same letter. They merge: رَدَّ: and come apart again before a consonant ending: رَدَدْتُ.
سَدَدَ → سَدَّ Past: heسَدَدَتْ → سَدَّتْ Past: sheسَدَدُوا → سَدُّوا Past: they (m.)يَسْدُدُ → يَسُدُّ Present: he