I need help with Questions 20 , 21 and 22 Please. Thank You,

Question 20 What assumption about the behaviour of total costs occurs within the relevant range of activity? linear and upward sloping linear and downward sloping curvilinear and upward sloping horizontal Question 21 Nextel Communications uses management by exception. Which differences between planned and actual results will it investigate? those that are material and non-controllable those that are controllable and non-controllable those that are material and controllable all differences should be investigated