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
Epithelial mesenchymal interaction in tooth development is an example of: 
Select and explain. 
A. Cell signaling, B. Calcification, C. Histodifferentiation, D. Morphodifferentiation
A: Cell signaling
Answer: A: Cell signaling 
Explanation: Cells interact through a system of effectors, modulators, and receptors called cell signaling. An example of such a system is epithelial-mesenchymal interaction in tooth development. The precursor cells, odontoblast and ameloblast, establish a positional relationship by means of effectors and receptors that are on the cell surface.