To solve this problem, we need to identify the three primary regions of a transcription unit in DNA with respect to the upstream and downstream ends. Let's analyze the options:$\newline \bullet$Option 1: Inducer, Repressor, Structural gene$\newline$ - An inducer and repressor are regulatory molecules, not regions of a transcription unit.$\newline$ - This option does not correctly define a transcription unit.$\newline \bullet$Option 2: Promoter, Structural gene, Terminator$\newline$ - The promoter is the upstream region where RNA polymerase binds to initiate transcription.$\newline$ - The structural gene is the region that is transcribed into RNA.$\newline$ - The terminator is the downstream region where transcription ends.$\newline$ - This option correctly defines the three regions of a transcription unit.$\newline \bullet$Option 3: Repressor, Operator gene, Structural gene$\newline$ - A repressor is a regulatory protein, and an operator is a regulatory sequence, not part of the transcription unit's primary regions.$\newline$ - This option does not correctly define a transcription unit.$\newline \bullet$Option 4: Structural gene, Transposons, Operator gene$\newline$ - Transposons are mobile genetic elements, and an operator is a regulatory sequence, not part of the transcription unit's primary regions.$\newline$ - This option does not correctly define a transcription unit.$\newline$Therefore, the correct option is Option 2: Promoter, Structural gene, Terminator.