Females are A. XX. Males are XY :)
Edwin Hubble used the Doppler effect to determine that the universe is expanding. After years of scientific research and observation of different celestial bodies through a telescope, Hubble found that the light from distant galaxies was shifted towards the red end of the spectrum. This red shift indicates that stars are moving away from us and from each other. This phenomenon is called the 'expansion of the universe', also known as the big band theory.
The answer is D.
It is the most needed because if the waste of the body doesn't get removed then you will become very ill and possibly die.
Hope this helps! :)
