**Core Concept**
Polysulfide impression materials are a type of thermoplastic elastomer used in dentistry for taking impressions of the oral cavity. They are known for their dimensional stability and accuracy. The base paste of polysulfide impression materials typically contains a combination of monomers and other additives.

**Why the Correct Answer is Right**
The base paste of polysulfide impression materials usually contains a mixture of polyethylene glycol (PEG) and polypropylene glycol (PPG) as fillers. These fillers help to improve the flow and viscosity of the material, making it easier to mix and apply. The addition of PEG and PPG also enhances the dimensional stability of the impression material, allowing for more accurate reproductions of the oral cavity.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the base paste of polysulfide impression materials does not typically contain polyvinylpyrrolidone (PVP) as a filler. PVP is actually used as an additive in some dental impression materials, but it is not commonly found in polysulfide impression materials.
**Option B:** This option is incorrect because the base paste of polysulfide impression materials does not typically contain silica as a filler. Silica is a common filler used in some dental restorative materials, but it is not typically used in polysulfide impression materials.
**Option C:** This option is incorrect because the base paste of polysulfide impression materials does not typically contain calcium sulfate as a filler. Calcium sulfate is a common filler used in some dental impression materials, but it is not typically used in polysulfide impression materials.

**Clinical Pearl / High-Yield Fact**
When working with polysulfide impression materials, it's essential to follow proper mixing and handling techniques to ensure accurate and reproducible impressions. This includes mixing the base and catalyst pastes in a specific ratio and allowing the material to reach its working time before applying it to the oral cavity.

**Correct Answer:** C.