Caresa Has a Somewhat Irregular Menstrual Cycle Ranging from 21

Caresa has a somewhat irregular menstrual cycle ranging from 21 to 35 days.Are Caresa and her partner good candidates for the Standard Days method of birth control?

A) No, because it is very difficult to accurately predict when she ovulates and therefore which days are "safe" from pregnancy.
B) No, because she may end up having intercourse near the beginning of her period, thereby increasing the likelihood of conception.
C) Yes, because not having to use any artificial means of birth control will greatly enhance their sexual satisfaction.
D) Yes, because an irregular menstrual cycle indicates that she is probably not fertile anyway.