From a competitive approach,principled negotiation may appear weak.According to the authors of your text,strength or toughness comes in the form of:

A) accommodating the other person in a negotiation.
B) firm flexibility.
C) standing up for your principles at all costs.
D) relying on criteria established by others.
E) inherent interests.

Principled Negotiation

A negotiation strategy that focuses on the merits of an issue and seeks mutual gains or objectives rather than positioning.

Firm Flexibility

The ability to be resolute in decision-making while being adaptable to changing circumstances.

Inherent Interests

Fundamental or natural concerns, desires, or motivations intrinsic to an individual or group.