the answer is decomposition.
90% of people weigh more than Nikoleta and 10% weigh less.
The controlled experiments are performed by the scientists, when they want to study the changes in the sample on changing a single variable. So, the correct answer is option (b).
In case, all variables are kept same, no changes would be observed in the experiment sample. A controlled experiment can be performed on living thing as well as non living. But, controlled experiment cannot be performed on the things which are influenced by a lot of variables, as they cannot create realistic results. So, the option (a), (c), and (d) are incorrect.
<span>If I were attempting to date a rock sample that I suspect to be incredibly old, i would use radioactive isotopes with a long half life. When dating rocks and fossils to discover approximately how old they are, radioisotope dating is used on igneous rocks found near fossils. Things like Uranium 235, which is an unstable radioactive isotope of elements, decays at a constant rate over time so can be useful in determining age.</span>