This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable Diseases, Subject name: Social & Preventive Medicine
[{'content': 'Incubation period of syphilis \nSelect and explain. \nA. 9-90 days, B. 9-18 days, C. 80-90 days, D. 10 days', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. a (9-90 days). (Ref. Harrison, Principles of Internal Medicine, 18th /Chapter 169. Syphilis)SYPHILIS# T. Pallidum enters foetal circulation after 20th week of gestation with disappearance of cytotrophoblast in villi.0# Basic pathology is obliterative endarteritis.# Placenta becomes bulky and spirochaete can hardly be found in placenta.# Spirochaete can however be detected from maculopapular rash in baby.# Irrespective of the serology, treatment should be repeated in subsequent pregnancies.# Incubation period of syphilis is 9-90 days', 'role': 'assistant'}]