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).