FCP2-480

A 25-year-old man presents with bloody diarrhoea associated with systemic upset. Blood tests show the following:

Hb 13.4 g/dl
Platelets 467 * 109/l
WBC 8.2 * 109/l
CRP 89 mg/l

A diagnosis of ulcerative colitis is suspected. Which part of the bowel is most likely to be affected?