By Interviews, Uncountable nouns

Hello. I need some help with celta preinterview task. II know the mistakes, however, I have no idea how to explain them easily. I'm new to all teachers' world so please help me :( I've got some ideas for the answers but the biggest problem for me is to explain to students so they...

I've just had a Celta pre-course interview, after which I was offered a place. The interviewer went through the language awareness task that I'd submitted and asked me how I would respond to a couple of questions that an efl student (beginner) might ask. One question I recall was, 'What is a...