I could title this “Spot the Difference” or “Respect Your Passing Partner”. I sent out three bidding problems to a panel of club players. Firstly let me give you the hand you are asked to bid, sitting WEST as was the case at the time:
You are West and Dealer at Nil Vul
Problem 1. You have opened 1S and North has overcalled with 2C. After two passes, it is your call. What should you be thinking? Why has partner PASSED?