Tropical forests contain dense trees, which allow less sunlight to penetrate. emergent trees are trees that grow to a height of more than 45 to 55 meters, above the usual height of trees in tropical forests. which system provides the best possible explanation for why these trees grow to those heights?
a: growth pattern
b: homeostasis
c: nervous system coordination in plants
d: phototropism

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".

in the year 2850, humans successfully colonized mars. the martian modules that were constructed could hold only a small population of people. it is now a century later, and the population on mars has grown to 600 people. of the current mars population, 45 people express the recessive phenotype for phenylketon- uria (pku) syndrome (pp genotype).

explanation: