Final answer:
Fat, sugar, and egg yolks contribute to a cake's moistness and richness, with fat adding tenderness, sugar providing sweetness and moistness, and egg yolks improving emulsification for a smoother batter.
Step-by-step explanation:
Fat, sugar, and egg yolks enhance the cake structure by providing moistness and richness. Fat, commonly coming from butter or oil, contributes to the cake's moistness and tender texture. Sugar not only adds sweetness but also moistness and works to tenderize the cake by interfering with gluten formation. Egg yolks contribute to the structure by emulsifying the fat and liquids, which aids in creating a smoother, more homogenous batter. This emulsification also contributes to the richness of the cake's flavor.