**Core Concept**
A recording base is a critical component in the fabrication of dental prostheses, serving multiple purposes in the process. It is a temporary base or plate that is used to support the tissues and allow for the accurate recording of the dental arch.

**Why the Correct Answer is Right**
The establishment of a VDO (Vertical Dimension of Occlusion) and VDR (Vertical Dimension of Rest) are essential functions of a recording base. It allows for the determination and recording of the CR (Centric Relation) by providing a stable base for the mandible to rest upon. This ensures accurate registration of the maxillary and mandibular teeth in the optimal occlusal relationship. On the other hand, checking for under/overextended borders of the final impression is not a function of a recording base, as it is typically done with a border seal or a border molding procedure.

**Why Each Wrong Option is Incorrect**
**Option A:** Establishment of VDR is a correct function of a recording base, as it helps in determining the optimal occlusal relationship between the maxillary and mandibular teeth.
**Option B:** Establishment of VDO is also a correct function of a recording base, as it aids in determining the correct vertical dimension of occlusion.
**Option D:** Determination & recording of CR is a correct function of a recording base, as it helps in registering the maxillary and mandibular teeth in the optimal occlusal relationship.

**Clinical Pearl / High-Yield Fact**
A recording base should be made from an impression material that is accurate, durable, and allows for easy removal from the mouth. The borders of the recording base should be carefully checked to ensure they are not under- or overextended, as this can affect the accuracy of the final impression.

✓ Correct Answer: C. For checking under/overextended borders of final impression