Which of the following techniques ensures that a value submitted in a form can only be yes or no?

Which of the following techniques ensures that a value submitted in a form can only be yes or no?

A.
Use a select list that only lets the user choose between yes and no.

B.
Use a hidden input field that has a value of yes or no.

C.
Enable thesafe_mode configuration directive.

D.
None of the above.