An important cause of ineffective or useless meetings is:

A) setting the rules for debate in advance.
B) restricting the meeting periods to 30 minutes or less.
C) the lack of preparation and planning.
D) following pre-established timetables.

The lack of preparation and planning is a major cause of ineffective or useless meetings. Without a clear agenda and objectives, meetings can quickly become unproductive and time-consuming. Setting rules for debate, restricting meeting periods or following timetables may help to keep the meeting organized, but they are not the primary cause of ineffective meetings.