This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Artifical radioisotopsa) Radiumb) Uraniumc) Plutoniumd) Iridiume) Cobalt 
Select and explain. 
A. ab, B. bc, C. de, D. bd
C: de
Answer: C: de 
Explanation: Important artificial radionuclides :- Tritium - 1, Carbon - 14, Cobalt - 60, Strontium 89, Strontium - 90, Iodine 131, Cesium 134, Cesium 137, Plutonium - 239, Iridium, Tc - 99.