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The correct answer would be through adaptation and eventually over time they had to evolve to the area around them which made them develop over time to have longer necks .
The five major types of estuaries classified by their geology are coastal plain, bar-built, deltas, tectonic and fjords. In geologic time, which is often measured on scales of hundreds of thousands to millions of years, estuaries are often fleeting features of the landscape.
The blood vessels farthest from the heart must have valves.
The valves which are present in the blood vessels prevent the backflow of the blood back into the specific organ.
There are different valves present in the heart are:
- The tricuspid valve is situated between the right atrium and right ventricle.
- The pulmonary valve is between the right ventricle and the pulmonary artery.
- The mitral valve is between the left atrium and left ventricle.
- The aortic valve is between the left ventricle and the aorta.
Other vales which are present in the blood vessels are in leg. Leg veins do require the valves. If not present the blood will go back down into the feet because of the gravity. Thus there are various valves present in the leg veins.
Valves in veins are bicuspid, meaning they have two flap-like structures that regulate blood flow in the vein.
To know more about the Valves, refer to this link:
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