They answer I gave were correct, but not elegant.
Sometimes there is a difference between the right answer and the right answer for the interview. You have to know both and try to work out which answer the interviewer is expecting.
Consider this question from the Oracle SQL Fundamentals Exam Guide
4. An entity-relationalship diagram shows data modelled into
A. Two-dimensional tables
B. Multidimensional tables
C. Hierarchical tables
D. Object-oriented structures.
The correct answer is B (which you will know if you have understood relational theory properly) the answer Oracle want to A, which is definitely wrong, but right if you want to pass the Oracle SQL Fundamentals Exam.
I don't know if Oracle have fixed this rather fundamental bug in their training material yet, but it's a bit of a showstopper.