What are the two most important nutrients for expectant mothers?

The correct choice emphasizes the importance of calcium and vitamins for expectant mothers. During pregnancy, calcium is crucial as it helps in the development of the baby’s bones and teeth, and also supports the mother's skeletal structure. Adequate calcium intake is essential to prevent complications like osteoporosis and to ensure the mother has enough reserves for breastfeeding after delivery.

Vitamins play a critical role as well. For instance, prenatal vitamins typically include folic acid, which is vital for neural tube development, preventing defects such as spina bifida. Other important vitamins include Vitamin D for calcium absorption and overall fetal development. These nutrients are pivotal not only for the mother’s health but also for the optimum growth and development of the fetus throughout the pregnancy.

Nutrients like protein and iron are also important, especially for blood volume increase and fetal growth, but they do not surpass the foundational roles that calcium and certain vitamins play during the critical periods of fetal development.