Final answer:
The best response by the nurse is that standing for long periods during the third trimester might increase ankle swelling, and it's essential to take regular breaks to alleviate pressure and reduce the risk of circulatory problems.
Step-by-step explanation:
The third trimester of pregnancy often involves increased discomfort due to rapid uterine expansion and other physiological changes. A pregnant woman who stands for long periods, like a cashier, may indeed experience more pronounced swelling of the ankles due to circulatory changes and increased pressure in the legs. Therefore, the best response by the nurse is D. "Standing might increase ankle swelling." Regular breaks are essential to alleviate this pressure and reduce the risk of circulatory problems, including clots which can arise from prolonged standing. While the nurse needs to inquire about regular breaks for eating and discuss the possibility of increased risks such as preterm labour, the most relevant immediate concern raised by the patient is related to standing and its association with swelling.