I think the answer is A. Competition. :)
Synapse plasticity
The ability of a given synapse to strengthen or weaken over time is known as synapse plasticity. The strengthening or weakening is in direct relation to the amount and way the synapse is used. The more frequently and vigorously a synapse is involved in activities, the more it will strengthen, just as in the case of muscles. This mechanism is important in learning and also lays the foundation of memory in the brain.
DNA is a dynamic and adaptable molecule. As such, the nucleotide sequences found within it are subject to change as the result of a phenomenon called mutation. Depending on how a particular mutation modifies an organism's genetic makeup, it can prove harmless, helpful, or even hurtful
It is four times dimmer than the sun.(4)
