According to the passage, platelets are LEAST likely to contain:
A transmembrane serotonin transporters.
B ribosomes.
C serotonin.
D Ki67.
Passage: "Platelets carry 95 percent of blood serotonin, which is synthesized from tryptophan and secreted by endocrine cells in the lining of the gastrointestinal tract. Researchers experimentally tested the hypothesis that platelet serotonin is responsible for the platelets’ positive effect on hepatocyte proliferation. The number of hepatocytes expressing the Ki67 protein, which is detected exclusively in the nuclei of proliferating cells, was used as a measure of liver regeneration."
