Final answer:
The most important response by the nurse to the pregnant woman's question about exercise during pregnancy is to ask what her usual type of exercise is.
Step-by-step explanation:
The most important response by the nurse to the pregnant woman's question about exercise during pregnancy is to ask what her usual type of exercise is (option D). This is crucial because it allows the nurse to assess the woman's current level of physical activity and provide tailored advice based on her individual circumstances. It ensures that the nurse can address any concerns or potential risks associated with the woman's specific exercise routine.