Welcome to your interview.
The question is on your right: Abstract Classes vs Interfaces. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
Explain the difference between abstract classes and interfaces in Java. When would you use each, and what trade-offs do they introduce in object-oriented design?