All four materials listed—agricultural residues, corn grain, wastewater treatment sludge, and wood mill waste—can be used as feedstock for producing Sustainable Aviation Fuel (SAF). Agricultural residues and wood mill waste are commonly cited as viable feedstocks due to their lignocellulosic content, which can be converted into biofuels. Corn grain is also used, particularly in processes that convert starches into ethanol, which can then be further processed into SAF. Wastewater treatment sludge is a less conventional but emerging feedstock, as it can be processed into SAF through various biochemical and thermochemical pathways. Therefore, all the materials listed can contribute to SAF production, making option 3 the correct choice.