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
During soldering, the solidus temperature of the filler material should be 
Select and explain. 
A. Greater than the substrate material, B. Lesser than the substrate material, C. Equal to the substrate material, D. Temperature not relevant
B: Lesser than the substrate material
Answer: B: Lesser than the substrate material 
Explanation: None