Final answer:
C. Efficiency
Efficiency is not involved in the project management triangle.
Step-by-step explanation:
The project management triangle, also known as the triple constraint or iron triangle, is a concept used in project management to illustrate the trade-offs between three key project aspects: Time, Resources, and Scope. The fourth option, Efficiency, is not directly involved in the project management triangle. Efficiency can be seen as a desired outcome of managing the project successfully, but it is not one of the three factors that need to be balanced.