Sprints promote iterative and incremental development.

This is a good answer because it is consistent with the Scrum Master's accountability to serve the Scrum Team and the organization by identifying and addressing the factors that hinder the team's effectiveness. By informing management of the organizational impediments, you can leverage their authority and influence to resolve them. By enlisting their help, you can also foster a collaborative and supportive relationship with them.
This is another good answer because it is consistent with the Scrum Master's accountability to educate and coach the organization on the Scrum framework and its principles. By explaining how velocity is used in Scrum, you can help management understand that it is not a reliable metric for measuring performance or comparing teams. By referring management to the Product Owner, you can also respect the Product Owner's accountability to manage the product backlog and communicate the value and status of the product34.

Explanation
The Scrum values of courage, openness, and respect are touched in this situation. Courage means that the Scrum Team members have the courage to do the right thing and work on tough problems, and also to speak up when they have concerns or disagreements. Openness means that the Scrum Team members and stakeholders agree to be open about all the work and the challenges with performing the work. Respect means that the Scrum Team members respect each other to be capable, independent people, and also respect the opinions and ideas of others.
In this case, the newest developer showed courage by expressing his feelings during the Sprint Retrospective, which is an opportunity for the Scrum Team to inspect itself and create a plan for improvements. The rest of the Developers should have been more open to listening to his perspective and ideas throughout the Sprint, as they might have valuable insights or suggestions for improving the product or the process. The Developers should also have respected the newest developer as a member of the team, and given him a fair chance to contribute and collaborate with them.
References:
The Scrum Guide, November 2020, p. 13-14
What are the 5 Scrum Values?, Visual Paradigm, accessed on September 30, 2023 Scrum Values Poster, Scrum.org, accessed on September 30, 2023

This is a good action to take, as it shows that the Scrum Team is willing to inspect and adapt their process and improve their collaboration and communication. The Sprint Retrospective is an opportunity for the Scrum Team to identify the root causes of the problem and create a plan for implementing improvements in the next Sprint.
This is also a good action to take, as it shows that the Scrum Team is flexible and adaptive, and does not let uncertainty or ambiguity prevent them from delivering value. The Developers can use the Sprint Goal as a guide to select and refine the Product Backlog items during the Sprint, and collaborate with the Product Owner to ensure that they are meeting the expectations and needs of the stakeholders.

Explanation
A: Arrange one-on-one coaching sessions where concerns the Scrum Master has identified can be discussed. This is a good way to provide individual feedback and guidance to the Scrum Team members and other people involved in the Scrum process. The Scrum Master can help them overcome any challenges or misunderstandings they may have about Scrum.
C: Schedule group training about Scrum. This is a good way to educate and inform a larger audience about the principles and practices of Scrum. The Scrum Master can use this opportunity to share their knowledge and experience with Scrum, and answer any questions or concerns that may arise.
E: Educate stakeholders and customers about Scrum. This is a good way to ensure that the people who have a stake in the product or service understand the benefits and expectations of Scrum. The Scrum Master can help them appreciate the value of empirical feedback, transparency, and collaboration that Scrum provides.
References:
Scrum Guide 2020, page 6: "The Scrum Master is accountable for establishing Scrum as defined in the Scrum Guide. They do this by helping everyone understand Scrum theory and practice, both within the Scrum Team and the organization." Professional Scrum Master II Course, page 8: "The role of the Scrum Master is to help everyone involved in creating products with Scrum to understand, apply, and improve upon the use of the framework."