Which of these is the foundation for relative dating?
a. earth is very old.
b. deeper rock strata are older.
c. radioisotopes decay at a constant rate.
d. organisms can be closely related to each other.

Which of the following types of pollution is most responsible for large numbers of deaths worldwide because of unsafe drinking water? (a) nutrient pollution (b) thermal pollution (c) pathogen pollution (d) sediment pollution