What is the molecular mechanism of action of growth hormone?

a. Growth hormone binds to specific receptors on target cells, which activates a signaling pathway that leads to the production of insulin-like growth factor 1 (IGF-1). IGF-1 then binds to its own receptor on target cells, which activates a signaling pathway that mediates the effects of growth hormone.
b. Growth hormone has no molecular mechanism of action.
c. Growth hormone directly enters target cells and activates a signaling pathway that mediates its effects.