Dr. delmar wants to determine how loud initially a certain noise must be in order for it to be heard from a distance of 60 feet. her question involves the concept of:

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.