(a) If the time for taking testimony by any party in the position of plaintiff has expired and it is clear to the Board from the proceeding record that such party has not taken testimony or offered any other evidence, the Board may grant judgment for the defendant. Also, any party in the position of defendant may, without waiving the right to offer evidence in the event the motion is denied, move for dismissal on the ground of the failure of the plaintiff to prosecute. The party in the position of