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
Silica sol: 
Select and explain. 
A. Is applied to the walls of the investment to produce hygroscopic expansion, B. Increase the strength and the setting expansion of the phosphate-bonded investments, C. Acts as a retarder in the silica bonded investments, D. Acts as a refractory in the silica bonded investments
B: Increase the strength and the setting expansion of the phosphate-bonded investments
Answer: B: Increase the strength and the setting expansion of the phosphate-bonded investments 
Explanation: None