Final answer:
Ms. R is lying in the Sims' position, which is used to support the abdomen and assist with contraction pains during the stages of labor.
Step-by-step explanation:
The correct answer to the position Ms. R is directed to lie in during labor is B) Sims' position. In the Sims' position, the person is lying on their side with one leg drawn up, often used in medical situations to support the abdomen or for rectal examination. This is none of the positions described in options a, c, and d, as the Sims' position is unique with the patient lying on their left side, having the right knee flexed, and the left arm positioned behind them. Labor involves three stages: cervical dilation, the expulsion of the newborn, and the delivery of the afterbirth (placenta). The Sims' position can aid comfort and assist with contraction pains during labor, promoting a smoother birthing process.