Final answer:
The correct answer is c) Heart rate decreases.
Step-by-step explanation:
During pregnancy, the mother's cardiovascular system undergoes several changes to accommodate the needs of the developing fetus. One of these changes is an increase in blood volume, which helps to manage the demands of fetal nourishment and waste removal.
Another change is an increase in stroke volume, which is the amount of blood pumped out of the heart with each beat. However, the heart rate actually decreases during pregnancy because the increased blood volume allows for a more efficient circulation of blood, reducing the need for the heart to pump faster.