The answer is A, a cell wall
All of the above points are valid for fossils' contributions in understanding the process of evolution. They allow us to study the ancestry, we can see the homologous organs or structures, if fossils are well-preserved; different fossils can lead us to follow the cycles of the changes that occurred during macroevolutions, and fossils can be used to study different populations which had different body structures for surviving in different environmental conditions.
Dna damage can occur as a result of exposure to chemicals or ultraviolet radiation. This is what happens during nucleotide excision repair of damaged dna. A multienzyme complex crosses the DNA in search of distortions in the double helix, once located, the phosphate skeleton of the affected chain is cut on both sides of the altered region, a helicase eliminates the oligonucleotide resulting from digestion, the "Gap" "is filled with a DNA polymerase and a ligase.
