I think it is natural selection. genetic variation also could be a factor for physical variation over the years.
3) 2) 1) i think this is the right answer but c looks correct too\
It is B , I know this thanks to the fact I took PE and our teacher teach us about the body !
You should never re-enter a burning building for belongings, animals, or people. Firefighters do that for you.
At SPF 23 the sunscreen start to interfere with vitamin D.
