The following table shows you which activities are available during each lesson.
Lessons 21 & 22 have no activities because the purpose of these lessons is to learn five key combinations [CTRL+C], [CTRL+V], [CTRL+S], [CTRL+Z], [CTRL+X] (For Macs, these are CMD) and do not require further activities.
Lessons 33 and 34 have no activities because these lessons are only available for Intermediate and Advanced levels.