Regarding the twin studies on intelligence, twins who develop from two separate eggs fertilized at the same time are known as __________ twins

Baby Hannah is shown a stuffed sheep, and then it is hidden under a blanket. Which of the following statements is true?

A) Hannah must coordinate two schemes to retrieve the object: "pushing" aside the blanket and "grasping" the stuffed sheep. B) Deliberately retrieving the stuffed toy is an example of a secondary circular reaction. C) Deliberately retrieving the stuffed toy is an example of a primary circular reaction. D) Hannah will not be able to retrieve the stuffed toy sheep until she is in Substage 5 of Piaget's sensorimotor period.

The ____ is a time during which organ systems are refined and begin to function

a. embryonic period b. fetal period c. period of the zygote d. implantation