d2 has game theory, both decision modules will really help you for the interviews, because they make you think about maths in a way the other modules dont, its that kind of approach to maths is what they look for in some economics/philosophy interviews so thatl be really good. And a simple awnser to your question is, if youve done single maths (as i have) they will only ask you c1-3, if you have done further then naturally they may want to test you on it. They are not going to ask you somthing youd have no clue on, its in neither your interest nor theirs so i wouldnt worry at all. Btw peaches when u went to catz did u have 2 interviews or one?