After reviewing the graph you have given with the question, there are several reasons why carbon 14 can't be used to accurately determine the age of organic remains that are 1 million years old.
A few of the reasons are; Carbon-14 has a short half life, after 1,000,000 years there wouldn't be enough carbon 14, and too little of the original radioactive sample would remain. Any of these choices are correct for the answer to the question you asked.
