Following injury to a blood vessel, immediate haemostasis is achieved by-: (A) Fibrin deposition, (B) Vasoconstriction, (C) Platelet adhesion, (D) Thrombosis
Answer is B. Robbins basic pathology, 9th edition, page no:79 Vascular injury primarily causes a transient aeriolar vasoconstriction through reflex neurogenic mechanisms augmented by local secretion of endothelin. All other options follow this. So the answer is option 2.