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
Elastomers are 
Select and explain. 
A. Alginate, B. Agar, C. Polyethers, D. Impression compound
C: Polyethers
Answer: C: Polyethers 
Explanation: According to Chemistry 
Chemically, there are four kinds of elastomers:

Polysulfide
Condensation polymerizing silicones
Addition polymerizing silicones
Polyether