Modular programming in AS/400 RPG uses three main techniques: /COPY compiler directives for including common source code, Subroutines for internal program modularization, and Procedures (also called subprocedures) which can be exported and shared across programs. Arrays (options A and B) are data structures, not modularization techniques. Option C correctly identifies /COPY, Subroutines, and Procedures as the modular programming techniques.