The human heart starts beating arounddays of embryonic development(. ) a) 22
b) 21
c) 23
d) 24

a) 22

Explanation:

Cardiogenesis which is the formation of the heart begins by day 21. The heart begins to form as paired tubes. By days 22 - 23 of embryonic development, the heart begins to beat. This represents the formation of the first vital organ of the body and it also causes the formation of left-right asymmetry of the body.

The days are counted from the day of the last menstrual period.

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.