Which estimation technique can be used in an Agile delivery approach to size the User...

In an Agile delivery approach, an estimation technique that can be used during sprint planning to size the User Stories is:

C. Relative estimates in Ideal Person Days that reflect the best estimates provided by the project team: This technique involves estimating the size of user stories relative to each other in terms of "ideal" days of work, assuming no interruptions for the person working on the story. This approach helps to gauge the effort and time required based on the team's experience and judgment.

Relative estimation helps the team to prioritize work and manage workload more effectively, relying on their collective expertise and past experience to provide realistic assessments.References:

Agile estimation practices

User story sizing in Agile projects

Agile Project Planning