Colonies are mutated in only one of four genes/sequences lad, lacO, lacZ or lacY, other genes/sequences are normal. When DNA from a lac mutant is transformed in to another lac mutant, it may complement function of mutated gene of recipient cell. In that case,the mutated genes of the two mutants are different genes. Otherwise mutants A and B are mutated in the same gene. In case of regulatory genes or sequences, nature of mutations may complicated interpretation of complementation test results, lacs mutant, for instance, cannot be complemented by any of the above mentioned mutations but lacOs.Presence of DNA from colony number 5 or 9 conferred all cells ability to utilize lactose,therefore, colony number 5 and 9 are lacOc mutants. Extra copy of lacOc mutant's DNA does not affect colony number 5 ability to grow on lactose, therefore, statement D is false.