I think it is the 3rd one because health problems at older age.
The central nervous system is made up of the brain and spinal cord<span>.</span>
Answer:
B. a food chain
Explanation:
Food chain: a hierarchical series of organisms each dependent on the next as a source of food.
Oxygen-16 and Carbon-12 are stableisotopes of elements O and C respectively. Hence, they do not have half-lives. But Carbon-14 andUranium-238 are radioactive isotopes. Among them Carbon-14 has relatively short half-life as about 5730 years while Uranium-238 has a long half-life as about 4.5 billion years.
Answer is. uranium-238
