please answer the question for number 3 "a" and "b"

19. In every array, a subscript is out of bounds when it is a. negative C. b. 0 You can access every element of an array using a a. while loop b. for loop d. 999 20. -. both of the above none of the above c. d. Exercises a. Design the logic for a program that allows a user to enter 15 numbers, then b. Modify the reverse-display program so that the user can enter any amount of a. Design the logic for a program that allows a user to enter 15 numbers, then 1. displays them in the reverse order of entry numbers up to 15 until a sentinel value is entered displays each number and its difference from the numeric average of the 2. numbers entered. b. Modify the program in Exercise 2a so that the user can enter any amount of numbers up to 15 until a sentinel value is entered. 3. a. Registratio n workers at a conference for authors of children's books have collected data about conference participants, including the number of books each author has written and the target age of their readers. The participants have written from 1 to 40 books each, and target readers' ages range from 0 through 16. Design a program that continuously accepts the number of