Concept:Each box can be used at most once, so we check which total can be formed as a subset sum.Explanation:The box weights are 30, 40, 50, and 80 kg.Option 120 is possible: 40+80=120.Option 110 is possible: 30+80=110.Option 130 is possible: 50+80=130.To get 100, no combination of 30, 40, 50, and 80 works.Therefore, 100 kg cannot be the total weight.Answer:100 kg, so option C.