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
[{'content': 'Base paste of polysulfide contains the following ﬁllers: \nSelect and explain. \nA. Silicon dioxide, B. Ferric chloride, C. Titanium dioxide, D. Barium sulfate', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The base paste, is a polysulfide polymer that contains a multi-functional mercaptan (-SH) called a polysulfide polymer, a suitable\xa0filler (such\xa0as\xa0lithopone\xa0or\xa0titanium\xa0dioxide)\xa0to provide the required strength, a plasticizer (such as dibutyl phthalate) to confer the appropriate viscosity to the paste, and a small quantity of sulfur, approximately 0.5%, as an accelera-tor. The catalyst (or accelerator) paste contains lead dioxide, filler, and plasticizer as in the base paste, and oleic or stearic acid as a retarder to control the rate of the setting reaction.\xa0\nLead dioxide is the component that gives polysulfide impression material its characteristic brown color. The terms catalyst and accelerator used here and with other impression materials are actually misnomers. Reactor is a more appropriate term for the reactions associated with polysulfide and other types of impression materials.\nKey Concept:\n\nRef: Phillips Science of Dental Materials Ed 12 Pg 153', 'role': 'assistant'}]