The statement that best summarizes Darwin's theory of natural selection is D. Organisms best suited to their environment will survive and reproduce. This is becasue let's say some giraffes have short necks and some long necks and their food is leaves on high trees then the long necked giraffes will survive over short necked giraffes because short necked giraffes can't reach for their food and eventually there will be only long necked giraffes left and they will reproduce with other long necked giraffes and make long necked giraffes.
D. introducing traits organisms
Durng meiosis, the chromosome number is halved.
as you climb higher in the atmosphere, there are three things that happen to your body, one is the circulatory affect, when there is hardly any oxygen in the blood, your body will start to react to this change in supply and either shut down, ((your lungs will give out, and you will pass out because of the lack of O2 in the brain)) or you will become Carbon-drunk. ((your cells will began to literally explode or shrink because of the fact there is no way to filter out your cells of the used up oxygen))
the second thing is with respiratory, your breathing will slow down and it will become hard to breath. its true that oxygen is lighter than carbon-dioxide, but oxygen is heavier then nitrogen and helium. Your body will start to feel heavier than normal and you will become weak. you will start to feel light-headed and eventually pass out if this feeling is new to you.
Third is the carbon affect, your body will end up dying because of it "reusing" carbon cells, and you will end up going into a coma because of the brain damage from no oxygen and too much carbon
GATCC is the correct nucleotide sequence.