[9급 국가직 영어 2020년 19번]

When an organism is alive, it takes in carbon dioxide from the air around it. Most of that carbon dioxide is made of carbon-12, but a tiny portion consists of carbon-14. So the living organism always contains a very small amount of radioactive carbon, carbon-14. A detector next to the living organism would record radiation given off by the carbon-14 in the organism. When the organism dies, it no longer takes in carbon dioxide. No new carbon-14 is added, and the old carbon-14 slowly decays into nitrogen. The amount of carbon-14 slowly (A) as time goes on. Over time, less and less radiation from carbon-14 is produced. The amount of carbon-14 radiation detected for an organism is a measure, therefore, of how long the organism has been (B) . This method of determining the age of an organism is called carbon-14 dating. The decay of carbon-14 allows archaeologists to find the age of once-living materials. Measuring the amount of radiation remaining indicates the approximate age.