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
Deciduous teeth do not show fluorosis because: 
Select and explain. 
A. Placenta acts as a barrier, B. Fluoride is taken up by the fast growing skeletal tissue, C. The calcification time of deciduous teeth is less, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Option 1: Placenta acts as a barrier.
Some authors have said that the placenta acts as a complete barrier to fluoride, others have said that it is only partial. Some have said that the placenta only acts as a barrier, when there is a sudden increase in the maternal plasma fluoride level.
Option 2: Fluoride is taken up by the fast-growing skeletal tissue.
Fluoride’s actions on bone cells predominate as anabolic effects both in vitro and in vivo. More recently, fluoride has been shown to induce osteoclastogenesis.
Option 3: The calciﬁcation time of deciduous teeth is less.