A 28 year old female teacher is found to have a prolonged bleeding time and normal platelet count. She had a bleeding of "easy bleeding" with frequent bleeding of the gums, epistaxis, cutaneous bleeding and menorrhagia, further testing revealed a deficiency of Von willebrand factor. Which of the following thrombogenic processes involving platelets is most directly impaired?
Adhesion Aggregation Formation of fibrinogen bridges Conformational change with activation of phospholipid surface