Select ALL the possible causes of a favorable overhead efficiency variance. The cost of indirect materials has increased due to supply chain issues The supervisor promised the assembly workers a bonus if they got the job out quickly Using higher-skilled workers than expected on the assembly line After receiving complaints about cheap materials, the purchasing manager purchased higher quality direct materials Participative budgeting resulted in budgetary slack Utility rates have increased due to recent tariffs on fossil fuels Poor maintainance of machines by the mainenance workers at the factory Inadequate training of assembly line workers by the production manager Cost of employer-provided healchcare for assembly workers has increased Overtime for assembly workers to finish a rush job