Замените формы глаголов Present Continuous формами глаголов Present Simple. 1. My relatives often spend much time together. 2. He usually teaches mathematics at school. 3. They visited a museum last Sunday. 4. Helen will meet her friend near the University tomorrow. 5. I will introduce my new friends to the parents tomorrow. 6. People set up a customhouse for the examination of foreign goods in 1749. 7. The fortress replaced the custom-house in 1761. 8. The inhabitants usually nickname the Don River as "Father Don". 9. People always call Rostov-on-Don the gateway to the Caucasus. 10. They will restore that church next year.

Вероятно вы имели ввиду заменить Present Simple на Present Continuous так, как глаголы уже написаны в форме Present Simple

1. My relatives are spending time together.

2. He is teaching mathematics at school.

3. They are visiting a museum today.

4. Helen is meeting her friend near the university today.

5. I am introducing my new friends to the parents today.

6. People are setting up a customhouse for the examination of foreign goods.

7. The fortress was replacing the custom-house in 1761.

8. The inhabitats is nicknaming the don river as Father Don.

9. People are calling Rostov on Don the Gateway to the Caucaus.

10. They are restoring that church.