If an outdoor runner develops a headache, feels tired, and has an elevated heart rate, what is the most probable cause?
a. insufficient calories
b. overhydration
c. dehydration
d. lack of protein

By 2 weeks after fertilization the morula has implanted into the uterine lining and transforms into a(n) . this time is when the , or the organ that will provide nourishment to the fetus by exchanging nutrients and waste products, begins to develop.