Loss of brca activity contributes to cancer because
a. without brca, dna damage-sensing kinases cannot establish a cell cycle checkpoint
b. without brca, cells cannot perform homology directed repair of double-stranded breaks
c. without brca, dna polymerase can't use its proof-reading activity
d. without brca, cells can't remove oxidized bases

synapse nervous system

it should be d) transitional fossils.

they show the gradualism of evolution throughout a period of time

increases the risk of extinction 

explanation:

the answer is that if the species suffers from the disease, there is nothing stronger than the others, so it is possible to remove wholeness. an example of this is hunger in irish potatoes, which has a deadly disease bearish part of all potato harvest masses. pretty much ruins the land of crops.