Organic foods are natural and are believed to protect from diseases and to be of higher quality. What is the MOST LIKELY factor keeping organic foods from completely replacing conventional foods?
A) greater cost
B) health concerns
C) environmental issues
D) greater availability

Ocean acidification is of considerable concern to environmental scientists as it could impact ocean biodiversity significantly. As carbon dioxide levels increase in the atmosphere, the diffusion of this gas increases in the oceans too. The formation of carbonic acid can impact species, as the lowered pH can cause weakening of shells made of calcium. Which of these species is not directly impacted by ocean acidification?
A) Sea turtles
B) Oysters
C) Corals
D) Clams