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
Occlusal caries index (ICDAS 1 and Histological Validation), code 4 means? 
Select and explain. 
A. Enamel demineralization Limited to outer 50% of enamel, B. Demineralization involving inner 50% of enamel upto DEJ, C. Demineralization involving outer 50% of dentine, D. Demineralization involving inner 50% of dentine
D: Demineralization involving inner 50% of dentine
Answer: D: Demineralization involving inner 50% of dentine 
Explanation: None