проверочное слово к слову участник

Ask people to help you in these situations. Example:You can't hear what the teacher is saying very well.-Could you speak louder,please? 1)You don't know what this word means. 2)You can't find your pen to write down a word. 3)You want to know the time. 4)You didn't understand what your parther said. 5)You want to leave a message for your friend.