This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
All the following are criteria to diagnose postmolar GTN except 
Select and explain. 
A. Plateau of serum b-hCG level (+- 10 percent) for four measurements during a period of 3 weeks or longer, B. Rise of serum b-hCG level > 10 percent during three weekly consecutive measurements or longer, during a period of 2 weeks or more, C. Serum b-hCG level remains detectable for 2 months or more, D. Histological criteria for choriocarcinoma
C: Serum b-hCG level remains detectable for 2 months or more
Answer: C: Serum b-hCG level remains detectable for 2 months or more 
Explanation: Criteria for Diagnosis of Gestational Trophoblastic NeoplasiaPlateau of serum b-hCG level (+- 10 percent) for four measurements during a period of 3 weeks or longer Rise of serum b-hCG level >10 percent during three weekly consecutive measurements or longer, during a period of 2 weeks or more Serum b-hCG level remains detectable for 6 months or more Histological criteria for choriocarcinomaReference: William's Obstetrics; 25th edition, chapter 20; Gestational trophoblastic diseases