The correct option is A Biological age
Coined by Charles Darwin, the term “living fossils” is used to describe living creatures that have stood the test of time — hardy and resilient organisms that have remained largely unchanged for millions of years. Radioactive C-dating is a method for determining the age of an object containing organic material by using the properties of C-14, a radioactive isotope of carbon.
Radioactive C-dating is used for biological age, geologic age and age of rocks but together with living fossils it is only used for biological age.