Correct answer:

The speed of onset determines whether the obstruction is acute, chronic or acute on chronic. In acute obstruction the onset is rapid and the symptoms are severe. In chronic obstruction the symptoms are insidious and slowly progressive (as, for example, in most cases of carcinoma of the large bowel). A chronic obstruction may develop acute symptoms as the obstruction suddenly becomes complete, e.g. when a narrowed lumen becomes totally occluded by inspissated bowel contents. This is termed acute-on-chronic obstruction.