Which of the Following Accurately Describes 13C/12C Ratios of Plant

Which of the following accurately describes 13C/12C ratios of plant materials and their use in climate reconstructions?

A) 13C is an unstable isotope,which decays at a constant rate.This is used to date plant material,which can then be used as a proxy for temperature and climate conditions at that time.
B) Different plants use different types of photosynthesis,each producing a different carbon isotope ratio in plant materials,which scientists use to determine past temperature and rainfall conditions.
C) By analyzing the ratio of 13C/12C in marine phytoplankton,the source of the water in which the organisms resided can be determined.
D) 12C is very rare in nature.When it does appear in plant material,it is indicative of climate anomalies.By measuring the 13C/12C ratios,scientists can determine whether the plants were alive during normal or anomalous conditions.