Final answer:
Undercuts for removable partial dentures are found in the infrabulge area of the teeth, below the height of contour, utilized for retentive purposes.
Step-by-step explanation:
When designing a removable partial denture, undercuts are found in the D. Infrabulge area of the teeth. Undercuts provide a natural retentive area that can help keep the denture in place. This area is located near the bottom of the tooth's crown, below the height of contour (or greatest circumference of the tooth), which allows the clasps of the partial denture to engage effectively. The design of partial dentures aims to use these undercuts to improve stability and retention without causing damage to the teeth or surrounding oral structures.