In a Kennedy Class I removable partial denture, where is the primary fulcrum line located?

In a Kennedy Class I (bilateral distal extension) RPD, the fulcrum line passes transversely through the most posterior abutment teeth on each side (the most distal teeth in the arch). This is critical for understanding denture biomechanics: when a force is applied to the distal extension bases, the denture rotates around this fulcrum line. This rotation causes vertical movement of the distal bases (tissue-ward) while the anterior indirect retainers move away from tissue. Understanding the fulcrum line helps in the design of clasps, rests, and indirect retainers to prevent denture rotation and maintain stability. The original question was incomplete and lacked meaningful options.