During agarose gel electrophoresis of dna, shorter dna molecules typically migrate faster than longer molecules. when closed-circular dna molecules of the same size possess different linking numbers, these dna molecules will also separate during agarose gel electrophoresis. a sample of purified plasmid dna of uniform length was separated on an agarose gel and stained, as shown below. in addition to a strongly stained band (b), the gel shows a faintly stained band (a) that migrated a much shorter distance. select the statement that explains why two bands appeared in the migration pattern.