Final answer:
The relationship between the Product Owner and Developers in agile development involves frequent collaboration to consider end-user and stakeholder concerns and make informed decisions about the product backlog items.
Step-by-step explanation:
B and C are the phrases that best describe the relationship between the Product Owner and the Developers. In agile development methodologies like Scrum, the Product Owner and Developers collaborate often to ensure that the end-user and stakeholder concerns are considered when building Increments. This collaboration allows the Product Owner to make informed decisions in balancing the effort and value of Product Backlog items.