Final answer:
The correct answer is c) Use the disabled property to gray out the box.
Step-by-step explanation:
The correct answer is c) Use the disabled property to gray out the box. By setting the disabled property to true for an input field, you can prevent the user from entering data into the box. This will visually gray out the box, indicating that it is not editable. The other options listed (a, b, and d) do not achieve the desired result of disabling user input.