Which of the following is an example of a functional requirement? Select the best answer.

Users must have a way to return to the main page from any other screen.

As users wait to visit the main page, a rainbow wheel image will appear on the screen.

When users select the $"$go back" option, it should bring them back to the main page in less than $5$ seconds.

When users select the $"$go back" option, it should bring them back to the main page quickly.