Explanation
The Scrum Guide states that "the moment a Product Backlog item meets the Definition of Done, an Increment is born" and that "the Increment is the sum of all the Product Backlog items completed during a Sprint and the value of the increments of all previous Sprints". Therefore, to deliver a product Increment that is integrated and potentially releasable, all Scrum Teams must have a shared understanding of what "Done" means and ensure that their work meets that standard. This also enables transparency, inspection, and adaptation across the Scrum Teams.
References:
The Scrum Guide, section 3.4 (The Increment), page 10
The Scrum Master Learning Path, module 5 (The Increment), lesson 1 (What is an Increment?) and lesson 2 (Definition of Done)

The Scrum Master is responsible for serving the team by facilitating and removing impediments to ensure there are minimal roadblocks in the way of the team. The Scrum Master also coaches the Scrum Team and organization to ensure the benefits of Scrum is realized.
"Removing every impediment for the Development Team" may seem like the right thing to do but by doing it this way, the Dev Team's ability to self-organize would be limited. There are some impediments that will depend solely on the Scrum Master and there will be some that require collaboration with the Dev Team. The former might be working with the finance department to renew services that the team is using. The latter might be lack of skills to make a particular item done. The Scrum Master can coach the team on finding different solutions to resolve the issue.
"Removing impediments" is good. "Removing every impediment for the Development Team" is not so good and sometimes not even possible.

Explanation
B: Productivity, in terms of lines of code or story points, will probably suffer during the transition, although even then delivery of business value is still likely to increase. This is a realistic expectation, as the teams will need to learn new skills, collaborate more effectively, and adapt to changing requirements. However, the benefit of feature teams is that they can deliver working software that provides value to the customers and stakeholders every Sprint, rather than waiting for the integration of different components.
C: Feature teams will require time to become productive as people from the different layers and components become accustomed to working and delivering unified functionality together, as one Scrum Team. This is a natural consequence of changing the team structure and culture, as the teams will need to overcome some challenges and conflicts, build trust and rapport, and establish a shared vision and goal. The Scrum Master can help the teams with this transition by facilitating communication, coaching, and mentoring.
References:
Professional Scrum Master II Course, page 17: "Feature teams are cross-functional teams that can deliver end-to-end functionality for a product. They have all the skills and competencies needed to work on multiple layers of the system." Professional Scrum Master II Course, page 18: "Component teams are teams that specialize in one layer or component of the system. They often depend on other teams to deliver a complete functionality for a product." Professional Scrum Master II Course, page 19: "Feature teams have many advantages over component teams, such as faster feedback, higher quality, lower complexity, and more customer value."

Scrum is a framework with built in flexibility to support multiple Scrum Teams working on a single product.