select ALL the statements that are TRUE

Consider the following method 1.double calculateBill(int usage)\{ 2. double bill = 0; 3. if (usage >0){ 4. bill =40; 5. \} 6. if (usage >100){ 7. if (usage =100){ 13. bill = bill 0.9; 14. } \} 16. return bill; 17. } Select all the statements that are true (1,4) is a DU pair for "usage" The use of "bill" in line 13 is a p-use (12,13) is a DU pair for "bill" The use of "usage" in line 8 is a c-use (4,8) is a DU pair for "bill