A physical therapist is following a 20-year-old female with a diagnosis of low back pain. During a scheduled physical therapy visit, she reports she has nausea and diarrhea that just began yesterday and that it kept her up in the middle of the night. She has taken antacids for relief. She now complains of right and left lower quadrant abdominal pain. The therapist decides to examine her abdomen through auscultation and palpation. The therapist confirms the patient has hyperactive bowel sounds and guarding of the abdomen. The therapist is correct in determining the client needs to be referred for follow-up secondary to suspicion of which of the following DIAGNOSES?

a) viral gastroenteritis
b) pneumoperitoneum
c) appendicitis
d) pelvic inflammatory disease