This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Growth and development, Subject name: Pediatrics
At which age does an infant hold its head steady when pulled to sit, without bobbing motion, and laugh and loud? 
Select and explain. 
A. 2 months, B. 4 months, C. 5 months, D. 6 months
B: 4 months
Answer: B: 4 months 
Explanation: At 3 months, head lag is paially compensated but still present; the infant attains early head control with bobbing motion and sits with back rounded. At 4 months, there is no head lag when pulled to sit and the infant sits with full truncal suppo. Ref: Nelson textbook of pediatrics 21st edition Pgno: 132