Which of the fontalle is the last to close after birth: (A) Anterior fontanelle, (B) Posterior fontanelle, (C) Sphenoidal fontanelle, (D) Mastoid fontanelle
Answer is A. Ref. The Short Textbook of Pediatrics. Pg 550
 

Anterior fontanelle closes  around 10-18 months
Posterior fontanelle closes around 8 weeks
Persistent posterior fontanelles is earliest sign of hypothyroidism