In the classification of angiosperms, which of the following features is crucial for distinguishing between the angiosperm families Ulaceae, Rosaceae, Fabaceae, and Brassicaceae?
A) The number of chlorophyll layers in the leaf.
B) The type of root system present in the plant.
C) The structure and arrangement of flowers, including petal number, symmetry, ovary position, and fusion of flower parts.
D) The presence of secondary metabolites in the plant.