Final answer:
The RPO and LPO projections will best demonstrate the posterior (ilioischial) column and anterior (iliopubic) column of the pelvis.
Step-by-step explanation:
The positions that will best demonstrate the posterior (ilioischial) column and anterior (iliopubic) column of the pelvis are the RPO and LPO projections. These positions allow for a clear visualization of the lesser sciatic notch and greater sciatic notch, which are the landmarks that represent the posterior column, as well as the anterior superior iliac spine and posterior superior iliac spine, which represent the anterior column.