Refertotheexhibit.Whichoptioncorrectlydescribestheorderofsignalingandcall processingeventswhenabranchemployeecallsheadquarters?()

A.P，S，T，U

B.U，T，S，P

C.S，U，P，T

D.P，U，S，T

E.S，P，U，T

F.S，P，T，U