Despite not providing the picture, there is enough information in the question to understand that the correct answer is alternative A) "At least 500 Million Years"
If the fossilized being lived around 500 million years ago, it means that the rock must be at least about that age.
Alternatives B and C are inconclusive, since the rock might have formed before, and with the information presented it's impossible to tell it's exact age. We can only tell that it's at least 500 million years old because of the fossil of a specimen that lived about 500 million years ago.
