An embryo transitions into a fetus at about week 9 during a pregnancy.
In the first three months the embryo goes through organogenesis and develops bodily organs, its heart starts beating after the fourth week, brain waves can be monitored after six weeks, and by the eighth week all major body parts are present. After the eight weeks, the embryo becomes a fetus.
(Sorry, I know these aren't the answer choices, but I hope this helps)