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.

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explanation:

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imagine a line passing through the center of earth that goes through both the north pole and the south pole. this imaginary line is called an axis. earth spins around its axis, just as a top spins around its spindle. this spinning movement is called earth's rotation. at the same time that the earth spins on its axis, it also orbits, or revolves around the sun. this movement is called revolution.