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
Which of the following procedure is indicated to produce cross-linking in the polymerization of linear chains of acrylic: 
Select and explain. 
A. Addition of grain refining agents, B. Addition of difunctional monomers, C. Increasing the amount of heat required for linear polymerization, D. Incorporation of terminating agents
B: Addition of difunctional monomers
Answer: B: Addition of difunctional monomers 
Explanation: None