Common mistakes
The second and third radicals are the same letter. They merge: رَدَّ: and come apart again before a consonant ending: رَدَدْتُ.
مَسَسَ → مَسَّ Past: heمَسَسَتْ → مَسَّتْ Past: sheمَسَسُوا → مَسُّوا Past: they (m.)يَمْسَسُ → يَمَسُّ Present: he