This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anatomy, Development and clinical examination, Subject name: Ophthalmology
Normal 6/6 visual acuity is attained at 
Select and explain. 
A. 6months, B. 1years, C. 3years, D. 6years
D: 6years
Answer: D: 6years 
Explanation: Development : 1 month - Fixation of light becomes more steady: Baby develops a preference for looking at the face or face-like-stimulus. 3 months - Binocular vision and eye coordination are established: Baby smiles in response to a visible smile: recognizes familiar faces and objects. 6 months - Preference for looking at human faces: ability to reach out, grasp and play with small objects 9 months - Looks for a toy if they see it being hidden. 6 years - Normal resolution visual acuity levels, such as that of adults, i.e. 6/6, 20/20 is attained. Ref. : Parson's Diseases of the Eye: 21st Ed; Pg. 27