Which of the following statements about platelets is NOT correct?

a) Platelets are small cell fragments derived from large megakaryocytes

b) Platelets release fibrinogen once a platelet plug is formed

c) Platelets adhere to the exposed collagen of a damaged blood vessel wall

d) Aggregated platelets release ADP, which participates in a positive feedback loop

e) Platelets release serotonin which causes the injured blood vessel to constrict