A gable end frame that extends outward over brick veneer can be formed by using lookouts and blocking attached to a ______.

The correct choice is a ledger because it serves as a structural element that is fixed horizontally to the building, providing a strong and stable base for the lookouts and blocking. This framing technique is crucial in supporting the gable end, especially when it extends outward beyond the brick veneer. By attaching lookouts to the ledger, builders ensure that the overhanging portion of the gable end is adequately supported, allowing for proper load distribution and structural integrity.

Using a ledger is an effective solution in this situation because it integrates seamlessly with the overall framework of the structure, particularly in gable designs where heavy loads and weather elements can affect the framing. In contrast, rafter and beam options do not provide the same horizontal support needed to effectively secure lookouts for extending gable ends, and a junction box is irrelevant in this structural context as it's associated with electrical installations rather than framing.