Physical chemists study matter and energy, and there is chemical reactions in your body, and all living things have elements, like carbon.
I would say D
The study of human interaction with the natural world over time is environmental history, emphasizing the active role that nature plays in influencing human affairs and vice versa. ... The first, nature itself and its change over time, includes human physical impact on the land, water, atmosphere, and biosphere of the Earth.
Fossils can give information about past environmental conditions by showing the type of animal they belonged to. If a scientist found a whale fossil in a desert, he/she could assume that the desert was once an ocean as whales only live in oceans. If someone found a fossil of a lizard that inhabited trees, in the middle of the ocean, then he/she could assume that the ocean didn't exist at one point and instead, there might have been a forest in it's place.
Hope this helps!
After hundreds or even thousands of generations both alleles for sickle cell anemia are still common in those of African ancestry. This is supported by two mechanisms: heterozygote advantage and gene flow.
Heterozygote advantage
When an allele is said to be heterozygous, it is carrying one copy of a gene. For example if one carries a copy of sickle cell allele, it will stay in the population even after many generations — natural selection will not be able to remove it and it will be passed on through generations. So, having one copy of that allele is advantageous but not deleterious.
Gene flow
With humans migrating throughout the different parts of the world, sickle cell allele is passed from one person to another or in different populations. It is actually advantageous to have one copy of this allele especially if there’s malaria in the area, which the allele is resistant.
There is only one structure feasible for a tetrahedral molecule with such a formula, under the supposition that A is in the center of the tetrahedredon. In this case X and Y are in the vertices of the tetrahedron.
If you draw several figures changing the position of the X's and the Y around the center (A), you will see that all are equivalent.
This is the case of the product CH3Cl, named chloromethane, which, for the same reason given above, does not have isomers.
