Final answer:
The classic presentation of an ovarian cyst causing torsion of the adnexa is acute onset of pelvic pain.
Step-by-step explanation:
The classic presentation of an ovarian cyst causing torsion of the adnexa is b) Acute onset of pelvic pain. When a cyst in the ovary twists, it can cause sudden and severe pain in the pelvic region. This pain often requires medical attention. Other symptoms may include nausea, vomiting, and fever.