The figure shows a dough that has risen after yeast was added to flour, warm water and sugar.  The BEST explanation for why the dough rises is:
AYeast adds water to the flour
BYeast reproduces and produces carbon dioxide during respiration, which fills the dough with bubbles
CYeast heats the dough up and causes it to expand thermally
DYeast converts flour into proteins which expand
Answer & Solution
Correct answer: B. Yeast reproduces and produces carbon dioxide during respiration, which fills the dough with bubbles
In warm, sugary dough yeast reproduces rapidly and respires, releasing CO₂. The trapped CO₂ bubbles increase the volume of the dough — the textbook calls this the basis of yeast use in baking.
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