Complete the sentences with the correct forms of the verbs in the present perfect.

1. We (join) _______ that project.

2. I (play) _______ a computer game at his house once.

3. She _______ never (work) _______ in such an unpleasant workplace.

4. He _______ never (be) _______ a class monitor.

5. They (go) _______ birdwatching several times.