Execution of conventional Procedure Call and returns D Fig. 21.3 shows a conceptual model of execution that explains flow of control during procedure call and return DA Single thread of control(execution) begins in the main program, passes through procedure a and B, and eventually returns to the main program14 Execution of Conventional Procedure Call and Returns Fig. 21.3 shows a conceptual model of execution that explains flow of control during procedure call and return A single thread of control (execution) begins in the main program, passes through procedure A and B, and eventually returns to the main program