Im not knowing of this subject but i'm sure your answer is C.) Patterns
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Answer:Valves stop blood flowing backwards
Explanation: Valve are flags of tissue that control the direction of the blood in our heart.,it prevent the backwards flow of blood. valves regulate blood from flowing back into the atria.The right and left atrio-ventricular valves prevent blood from flowing backwards into atria. When the ventricle is full,the valve prevent backwards flow of blood.
Answer:
grams
Explanation:
Given -
Half life of the silicon-32
years
Half life means the time period required by a radioactive element to reduce its mass by half.
Radioactive decay formula is

Where
A represents the amount of radioactive element after time t years
represents the initial amount of radioactive element
time of decay
half-life of the substance
Substituting the given values in above equation, we get -

grams