You notice that some E. colicultures failed to grow in the presence of only lactose. You know that normal E. coliare able to metabolize lactose so something must be wrong. Which mutation (s) could explain this

The correct answer is "mutations in the lac operon or in the promoter region".

Explanation:

The lac operon es a series of genes that are translated and expressed simultaneously, allowing the cell to metabolize lactose when glucose is absent. The E. coli cultures that failed to grow in the presence of only lactose, could have a mutation that affects the lac operon. This mutation could be present in the promoter region or in the lac operon itself, which will result in the absence of lac operon transcription or in the transcription of one or more non active protein, respectively.