Here are the correct forms of the bracketed words:

1. There are a lot of interesting extra-curricular **activities** for students in my school. (act)
2. I am sorry for any **inconvenience** this change in the schedule may cause you. (convenient)
3. Kids in the city enjoy their **playtime** differently from kids in the countryside. (please)
4. Some ethnic groups in our country use their own **languages**. (speak)
5. There are many cultural **differences** between his country and mine. (differ)