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
[{'content': 'M in 99Tc"\' stands for? \nSelect and explain. \nA. Micro, B. Mega, C. Metastable, D. Metastatic', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Metastable REF: Nuclear Physics: Principles And Applications by Lilley Page 20 "In 99Tcm the superscript M denotes that the technetium 99 is not in its ground state but a long lived metastable excited state"', 'role': 'assistant'}]