The tricuspid valve shuts. This prevents blood from flowing backward into the right atrium while the ventricle contracts. So, your answer will be the Tricuslid Valve. Hope I helped!
The answer to this question would be D.) Permafrost prevents penetration of deep roots.
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Answer:
The answer would be C. This is because the nucleus of a cell is responsible for the creation of ribosomes. Hope this helps you :)
Bio hazard since it's used as a pesticide