According to Kepler's model of the solar system, what is retrograde motion is caused by? Select one: a. epicycles. b. the daily turning of the celestial sphere. c. the difference in orbital speed of Earth and other planets. d. the changing speed of the Sun. e. the Earth's rotation.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".

if you add everything up correctly you should get 69 i got this because 50 plus 19 is it