Circulation is your blood flow, well in my words. Like for example "I'm losing circulation in my arm." They are having their blood flow slow down or even stopped. It doesn't always have to be blood, it can be any fluid
Nitrogen, oxygen, carbon, hydrogen make up amino acids(subunits of proteins). Some aminoacids have sulfurous in their R group.
I think the answer is A. Competition. :)
Squamous cells area one single layer and flattened, this allows for diffusion of oxygen and carbon dioxide to happen easily in the lungs.
