What is the current known role of complexin in synaptic transmission?A、 Complexin makes sure vesicles are near Ca2+ channels.B、 Complexin binds vesicles to scaffolding proteins in the presynaptic membrane.C、 Complexin clamps the SNARE complex in an intermediate step prior to vesicle fusion.D、 Complexin is required for presynaptic Ca2+ channels to open.