Answer: changes in project scope
Step-by-step explanation:
Project scope is the planning of how a particular project will be accomplished, which includes highlighting and properly stating the project goals, documenting the quantity and quality of materials needed, costing, scheduling tasks, and setting deadlines.
In the case above the manager has already started the project which has an existing plan, then realises that some changes had to be made, after obtaining more information and understanding about the project.
Therefore the project scope had to be revised.