plz quickly

Question (1): Based on what you have studied about Quantitative Analysis, answer the following questions: (6 marks) a. Choose the correct answer of the following: 1- What is the essential condition for using the graphical method? a. Negative variables. b. Integer variables. c. Only two decision variables. d. More than three variables. 2- In LP, numbers in the objective and constraints are always known and do not change during the period being studied. This assumption is called a. Proportionality. b. Additivity. c. Divisibility. d. Certainty. 3- In solving a linear program, no feasible solution exists. To resolve this problem, we might a. Add another variable. b. Add another constraint. c. Remove or relax a constraint. d. Try a different computer program