After conception, the main organs are established by the end of the
(a) third day.
(b) second week.
(c) eighth week.
(d) fourth month.

it should be briana that has it to me

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".