The correct answer is C, because as soon as possible in the Sprint, the Development Team should work with the Product Owner to remove some work or Product Backlog items if they realize they have selected too much work to finish in the Sprint. The Scrum Guide states that "the Development Team may renegotiate the selected Product Backlog items with the Product Owner. If the Development Team realizes it has too much or too little work, it may renegotiate the selected Product Backlog items with the Product Owner. The Development Team may also invite other people to attend to provide technical or domain advice."

When a Development Team determines that it will not be able to finish the complete forecast, both the Product Owner and the Development Team have to be present when reviewing and adjusting the Sprint work selected, as stated in [6]: "If there is not enough work remaining for all members of a Development Team then they can renegotiate scope with their Product Owner. If there is too much work remaining then they can also renegotiate scope with their Product Owner."

The correct answer is B, because the guideline that a Scrum Master should give is that estimates are made by the Development Team. The Scrum Guide states that "the number of items selected from the Product Backlog for the Sprint is solely up to the Development Team. Only the Development Team can assess what it can accomplish over the upcoming Sprint." Therefore, the Development Team should estimate the work in Scrum, using any method or unit they prefer.