What's the most difficult question you were asked during your interview for Cambridge?

During my second interview, the interviewer asked me to compare language with a city, meaning I had to use components of a city or town in order to describe how the structures of a language worked. I told the interviewer I wanted a few minutes to think, which they were happy about, so I wasn't rushing into my answer. I then explained how I would make the transport system "grammar", because grammar enables us to connect individual words together to form a sentence. I said that I would therefore make the buildings the individual words, and the interviewer asked me to specify what kinds of words each building would be. I then explained that content words, like nouns, could be skyscrapers, because they tend to form the overall meaning of the sentence, whilst function words, like verbs, could be buildings like libraries, museums and buildings like this that are used to learn, because function words glue the sentence together and complete its meaning. The interviewers were mostly interested in how my mind worked and how I articulated my thoughts. So, although this was a tricky question, it was less about my actual answer and more about how I got to my answer.