Remarkably, biologists are able to extract DNA from fragments of ancient Neanderthal bone and sequence Neanderthal DNA. Biologists are also able to come up with an accurate age of the remains. Some of these remains are as recent as 28,000 years old. What of the below is true about how they age the remains?

a. All of these
b. By extrapolating the half-life of Carbon-14 to estimate how much time the ratio of Carbon-14 to standard carbon took reach the present value in the bone
c. By measuring the amount of Carbon-14 present in the bone
d. By comparing the ratio of Carbon-14 to standard Carbon in the bone