Which of the following is the "regulated membrane transfer"?

Regulated membrane transfer is the transpo across/through the membrane which is regulated by a specific signal or ligand. Exocytosis is a regulated membrane transfer. E.g. Neurotransmitter secretion at a synaptic junction. The transmitter is released only when the signal/impulse arrives at the nerve terminal. Insulin secretion, by exocytosis, occurs when a signal, i.e. increased blood glucose, is delivered to the pancreatic beta cell. Options (B), (C), and (D) do not occur after a specific signalling ligand has arrived at those respective cells.