Final answer:
Hormonal changes during pregnancy can slow down digestion, causing constipation. The growing uterus can also put pressure on the rectum, exacerbating the constipation.
Step-by-step explanation:
The nurse should respond with option C) "Hormonal changes during pregnancy slow down digestion." Hormones such as progesterone and estrogen, which increase during pregnancy, can affect the muscles in the digestive system, causing them to relax. This relaxation can lead to slower food movement through the intestines and result in constipation. The growing uterus may also put pressure on the rectum, further contributing to constipation.