Answer:
C
Explanation:
Many kinds of air pollution can't be seen, which means A is incorrect. Any kind of pollution can be harmful to you, which means B is incorrect too. Air pollution is very harmful but in most cases can't be directly seen, so C is correct. Pollution can be found everywhere, so D is incorrect also.
Sure what is it , where is it
sodium-potassium pump. n. The enzyme-based mechanism that maintains correct cellular concentrations of sodium and potassium ions by removing excess ions from inside a cell and replacing them with ions from outside the cell.