Answer: b) common features.
Explanation: Classification is the way we decide on relationships between groups of organisms, and this is done in several levels in a hierarchy. For example, all plants form a group based on having chlorophyll and being photosynthetic (the plant kingdom), which other kingdoms like animals and fungi do not. Within plants there are divisions, like angiosperms - plants with flowers. The closest relationships are between species in the same genus, plants that have the same kind of flowers and seed, like the Flanders poppy and California poppy.