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: Dental
According to Mahler's theory, period of normal symbiotic phase is: 
Select and explain. 
A. 0 - 1 year, B. 4 weeks to 4 years, C. 8 weeks to 8 years, D. 5 to 36 months
B: 4 weeks to 4 years
Answer: B: 4 weeks to 4 years 
Explanation: According to Mahler's theory:

The normal autistic phase is 0-1 year.
Normal symbiotic phase is 4 weeks to 4 years.
Separation individualization phase is 5 to 36 months.