Refer to the exhibit. Which option correctly describes the order of signaling and call processing events when a branch employee calls headquarters?()<br /> <img src="https://nimg.ppkao.com/2018-07/zhanglijun/2018072416205564566.jpg?sign=42f811ac96b150fde586300ac1de28e7&t=62d0a6de" />
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