Conditional activities http://docs.moodle.org/en/Conditional_activities is a new feature in Moodle 2.0 :
* Access to activities can be restricted based on certain criteria, such as dates, grade obtained, or the completion of another activity.
* These can be chained together to enable progressive disclosure of the course content, if that is desired.
* Teachers can now specify conditions that define when any activity is seen as completed by a student. For example, when a certain number of posts have been made, or a grade has been reached, or a choice has been made Less