This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Intra Uterine Growth Restriction, Intrapaum and Antepaum Fetal Surviellance, Subject name: Gynaecology & Obstetrics
[{'content': 'The Kleihauer Betke test for detecting foetal erythrocytes is based on the fact that \nSelect and explain. \nA. Adult erythrocytes are larger than those of foetus, B. HbA has higher oxygen affinity than HbF, C. HbF is more resistant acid elution than HbA, D. HbA takes up erythrosin stain less than HbF', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The most commonly used quantitative test for fetal red cells in the maternal circulation is the acid elution or Kleihauer Betke test. Fetal erythrocytes contain HbF, which is more resistant to acid elution than HbA.', 'role': 'assistant'}]