The correct option is A C14 and O18
Oxygen-18 is a natural, stable isotope of oxygen. Oxygen 18 was used to give an insight into photosynthesis, as it allows the amount of oxygen taken up during photosynthesis to be measured and showed, where the oxygen came from and from where it ended up. Carbon-14 is a radioactive isotope of carbon, naturally found in the stratosphere and troposphere and is used in radiocarbon dating to date an archaeological, geological and hydrogeological samples.