what does this mean? "DNA is in its composition characteristic of the species from which it is derived. This can ... be demonstrated by determining the ratios in which the individual purines and pyrimidines occur There appear to exist two main groups of DNA, namely the 'A-T type,' in which adenine and thymine predominate, and the 'G-C type,' in which guanine and cytosine are the major constituents."

African penguins, which inhabit the coasts of southern africa, were classified as an endangered species in 2010. two significant threats to their survival are ecosystem damage from oil spills and overfishing by humans. overfishing depletes the food supply of african penguins. the best method to reduce the threat of overfishing would be to . the risk of oil spills could be reduced by increasing the use of , which should oil consumption. if an oil spill does occur, could be used to remove the oil so the ecosystem may more quickly recover.