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
Tooth structure cutting is preceded by crack propogation due to tensile forces known as: 
Select and explain. 
A. Brittle fracture, B. Ductile fracture, C. Shear fracture, D. All of the above
A: Brittle fracture
Answer: A: Brittle fracture 
Explanation: Tooth structure is cut by two types of fracture

Brittle fracture
Tensile fracture

Tensile fracture proceeds by plastic deformation due to shear forces.