Remotre Procedure Call (RPC) is the only of the above choices to operate at the session layer (layer 5).
All of the other answers were wrong.
LPD operates at layer 7
SPX operates at layer 4
IGMP operates at layer 3.
[Reference:, WALLHOFF, John, CBK#2 Telecommunications and Network Security (CISSP Study Guide), April 2002 (page 1). , , ]
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