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) Carbon is such a rare element on Earth that the 13C/12C ratios help scientists deduce glacial and interglacial cycles.
B) 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.
C) 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.
D) Scientists can determine if conditions were wetter or drier,warmer or cooler,but analyzing the ratio of 12C to 13C.
E) By analyzing the ratio of 13C/12C in marine phytoplankton,the source of the water in which the organisms resided can be determined.