The correct answer is D. All of these are commonly used radioactive isotopes in scientific research.
14C is a radioactive isotope of carbon with a half-life of 5,730 years. It is used to date organic materials, such as wood, bone, and paper.
125I is a radioactive isotope of iodine with a half-life of 60 days. It is used in medical imaging and therapy.
32P is a radioactive isotope of phosphorus with a half-life of 14 days. It is used in biological research and medical imaging.
Radioactive isotopes are used in scientific research because they can be used to track the movement of materials and to study the structure of molecules. They are also used in medical diagnosis and treatment.