Final answer:
The most appropriate button to confirm dinner reservations is 'Confirm Reservation', as it explicitly indicates the action of confirming an existing booking.
Step-by-step explanation:
To confirm dinner reservations, the student should look for a button that most closely matches the action they want to perform. Among the options, Confirm Reservation is the most straightforward and specific choice, as it directly indicates the action of confirming an existing reservation.
The other buttons such as Book Now or Reserve Table might be related to making a new reservation, and Submit could be used for any form submission.