The right answer is vein (it contains blood and has valves).
The infra-cardiac veins of small and medium caliber possess this system of fight against gravity. The valves consist of a dense connective tissue, surmounted by endothelial cells, corresponding to a fold of the intima. They allow blood circulation in the sense organ / heart but prevent venous reflux.
Answer:
where are the choices????
This is called a behavioral pattern. This is something deer have learned over time that gives them an advantage in the wild.
Answer:
A)Fixation. Nitrogen in its gaseous form (N2) can't be used by most living things
B) it can not be used because it most be converted or, ’fixed’ to a more useable form. To do this it goes through a process called fixation.fixation is the change in a gene pool from a situation where there exists at least two variants of a particular gene (allele) in a given population to a situation where only one of the alleles remains.
C) This form can be made more usable if it’s converted. It has to go through the process of fixation so the gene pool changes.
Explanation:
Rather than helping one species you can help a entire ecosystem. if you think about it, you would be saving more in a ecosystem then you would in just 1 single species
