Choice A rationale Applying a fetal scalp electrode directly measures the fetal heart rate (FHR) but is an invasive action and not the initial priority for addressing late decelerations. Late decelerations, often caused by uteroplacental insufficiency, necessitate immediate interventions to improve fetal oxygenation and perfusion before considering invasive monitoring. FHR baseline and variability are already visible on the external monitor, guiding initial management. Choice B rationale Increasing the rate of intravenous fluids, typically a non-oxytocin isotonic solution like lactated Ringer's, aims to increase maternal intravascular volume. This action may improve uterine perfusion and, subsequently, fetal oxygenation. While crucial, it often follows or is implemented concurrently with positioning changes to maximally improve blood flow dynamics. Choice C rationale Administering high-flow supplemental oxygen (10 L/min via nonrebreather) to the mother increases the maternal PO_2, thereby increasing the oxygen concentration gradient and improving oxygen transfer across the placenta to the fetus. This is a critical step in intrauterine resuscitation, yet position change is often the first, easiest, and quickest intervention. Choice D rationale Changing the client's position, usually to the left lateral side, is the primary and immediate intervention for late decelerations. This maneuver displaces the gravid uterus off the inferior vena cava and aorta, reducing aortocaval compression and improving venous return, cardiac output, uterine blood flow, and uteroplacental perfusion. This action directly addresses the most common etiology: uteroplacental insufficiency.