Rectification is energy demanding. The reboiler requires heating utilities and the condenser requires cooling utilities. Some of the sketched column configurations do not fulfill any separation task. Thus, they can be regarded as "just a waste of energy"!
Tick those sketched rectification columns, which do not fulfill any separation task. Pay attention! Configurations, which at first glance seem to be non-sense, might still fulfill a separtion task. The separation task is fulfilled, whenever the compositions of the outgoing streams differ from the feed composition.