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
A 45 year old male patient complains of food lodgment and pain in lower right back teeth region. RCT was done with 46. Cast metal restoration was planned for 46. Defective carbon inclusions were seen on the casting. All of the following factors are responsible for this defect except: 
Select and explain. 
A. Carbon-containing wax, B. Carbon from crucible, C. An improperly adjusted torch, D. Carbon-containing investment
A: Carbon-containing wax
Answer: A: Carbon-containing wax 
Explanation: CARBON INCLUSIONS
Carbon from a crucible, an improperly adjusted torch, or a carbon-containing investment, can be absorbed by the alloy during casting. These particles may lead to the formation of carbides or even create visible carbon inclusions.
Phillips’ Dental Material, pg- 225