Answer is C (Terminal ileum):'Classically there is obstruction / impaction about 60 cm proximal to ileocaecal valve'- Bailey'The site of obstruction by the impacted gall stone is usually at the ileocaecal valve" provided that the more proximal S.I. is of normal calibre. - HarrisonsIf both choices come simultaneously in a question go for 60 cm proximal to ileacoecal valve, as, it has been defined as the narrowest pa of small intestine.