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 phyyoplsnkyon, 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.