Why Do Some Bread Recipes Suggest Letting the Dough Rise

Why do some bread recipes suggest letting the dough rise in a warm place after kneading?

A) Warming the bread slightly before cooking it in a hot oven stretches out the gluten.
B) The metabolic rate of yeast speeds up at warmer temperatures,so more carbon dioxide is released and the dough rises more quickly.
C) The metabolic rate of yeast slows down at warmer temperatures,so more sugar is maintained and the bread is sweeter.
D) Yeast cannot carry out fermentation at room temperature.