Which one of the following statements is true regarding the stages of development?
A. The pre-embryonic stage involves the formation of a blastocyst.
B. The embryonic stage occurs after the 8th week of development.
C. Myelination occurs during the fetal stage of development.
D. Both A and C
E. All of the above
ANS: D
Rationale: In utero, humans undergo three stages of development. The pre-embryonic stage lasts from conception until day 14 and involves fertilization, as well as the formation and implantation of a blastocyst. The embryonic stage lasts from day 15 until the end of the 8th week, during which time the organ systems are formed. The fetal stage lasts from the end of the 8th week until birth, during which time the nervous system develops more fully and myelination occurs.
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