The Product Owner is also known as the value maximizer. He is responsible for maximizing the value of the work that the Development Team does. This is done through the ordering of the Product Backlog.

As a servant/leader, the Scrum Master facilitates conversations through open ended Question:s in order to help the team members make the best possible decisions according to what is known at the time. He/she does not approve or reject team decisions but ensures the team stays within the boundaries of the Scrum framework.

Explanation
B: Developers can artificially increase velocity by incurring technical debt. This is a true statement, as some Developers may choose to take shortcuts or compromise on quality in order to deliver more work in a Sprint. However, this is not a sustainable or ethical practice, as it will create more problems and costs in the future. The Scrum Master can help the Developers to avoid this temptation and focus on delivering value and quality instead.
D: Velocity may unexpectedly drop when the Developers run into technical debt while attempting to complete new Product Backlog items. This is a true statement, as technical debt can act as a drag on the productivity and progress of the Developers. Technical debt can make the work more difficult, complex, or risky, and may require more time and effort to fix or refactor. The Scrum Master can help the Developers to identify and manage technical debt, and communicate its impact to the Product Owner and the stakeholders.
References:
How Technical Debt Affects Your Velocity1
Understanding the impact of technical debt on the capacity and velocity2