Final answer:
The architect's cost of work estimates remain constant throughout the project.
Step-by-step explanation:
The correct answer is (a) Constant cost.
When the project manager is updating the cost of work estimate for the design development phase, the architect's cost of work estimates will remain constant throughout the project.
This is because the architect's cost estimation for the design development phase does not change as the project progresses. The estimate is based on the scope of work and the resources needed to complete the design development phase, which does not vary with the project timeline.