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
In cap stage, regulating factor for cusp shape formation is present in 
Select and explain. 
A. Dental papilla, B. Dental follicle, C. Inner enamel epithelium, D. Enamel knot
D: Enamel knot
Answer: D: Enamel knot 
Explanation: Enamel Knot: The cells in the center of the enamel organ are densely packed to form enamel knot.
Enamel cord: It is the vertical extension of the enamel knot.
Enamel Septum: The enamel cord extends to meet the outer enamel epithelium and form enamel septum.
Enamel Navel: It is the small depression at the point of meeting of enamel cord and outer enamel epithelium.
Enamel niche is the apparent structure created by the plane of histological sections cutting through a curved dental lamina so that mesenchyme is surrounded by the dental epithelium. It appears as a double attachment of dental lamina to the overlying epithelium.

Recent studies shows that enamel knot acts as a signaling center expressing growth factors which play an important role in determining the shape of the tooth