Which factor is not used to define biomes?
a.
plant structures
b.
leaf type
c.
historical similarities
d.
climate

The correct answer is - c. historical similarities.

The historical similarities do not play any role in defining a present day existing biome. The biome is defined by the living organism that interact between each other, and the physical environment where those organisms live.

The historical similarities can play a role in defining a biome of the geological past by carefully connecting the information available.

radiative zone

explanation    

radiative zone is the layer of the sun which energy is transferred away from the core by radiation. although, the core is the only part of the sun that produces an appreciable amount of heat through fusion. in fact, 99% of the energy produced by the sun takes place within 24% of the sun's radius.