The answer you are looking for is A
A valve is a flap of tissue that prevents blood from flowing back
The food substance being used which turned Fehling's solution to brick red is a reducing sugar.
<h3>What is Fehling's solution?</h3>
This is an indicator which is used to test for the presence of reducing sugar or aldehydes in a solution.
Brick red precipitate of copper(I) oxide is formed when it tests positive to compounds such as glucose etc.
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the answer might be 2.3 kilos
