Correct Answer: A, CTo meet the requirements, if the quantity (qty) is 90 or more, the discount should be 0.5, and if the quantity is between 80 and 90, the discount should be 0.2. Option A evaluates if qty is greater than or equal to 90 to set the discount to 0.5, and separately checks if qty is between 80 and 90 to set the discount to 0.2. This meets both requirements. Option C uses a ternary operator to achieve the same logic in a single line by checking if qty is greater than or equal to 90 first, then if it is greater than 80, and finally setting the discount accordingly. Options B, D, and E have logical errors or do not meet the requirements fully.