<prompt>  A 22 year old man presents with history of bleeding from gums for the last 6 months. On investigation the b was found to be 8.2 gm TLC 4400mm, DLC N 64, L 27, E 3, M 6 and platelet count of 20,000 cu mm. Which one of the following investigation would be most useful in establishing the diagnosis -Bleeding time and clotting timeProthrombin timePartial thromboplastin timeBone marrow examination 