Step 1: This is a negative-stem question - find the statement that is FALSE for Crohn's disease. Crohn's is a transmural, patchy inflammatory bowel disease that can affect any part of the gut from mouth to anus.
Step 2: A hallmark of Crohn's is discontinuous SKIP LESIONS - inflamed segments separated by normal-looking mucosa. So a continuous lesion on endoscopy is characteristic of ULCERATIVE COLITIS, not Crohn's. Option (b) is the untrue statement and is the answer.
Step 3: The other options are true of Crohn's: the rectum is typically spared (a), the disease shows non-caseating granulomas on histology (c), and the mucosa develops a cobblestone appearance from linear ulcers and oedema (d).
Step 4: Contrast: continuous involvement, rectal involvement and crypt abscesses point to ulcerative colitis, whereas skip lesions, granulomas, transmural disease and cobblestoning point to Crohn's. The false statement is the continuous lesion.