You are presented with the question "Radioactive isotopes are commonly used to do what to the age of fossils?" and the following answer choices: 
- duplicate itself
 - observe it
 - debate them
 - Temperature
 - Time and energy
 - determine them
 - remove them
 - assign them

Now knowing that radioactive dating is used to determine the age of fossils and radioactive isotopes are commonly used for dating , choose the best answer.


 

      determine them   