In The Prisoner of Glouphrie, if you didn't actually look at the picture of the Grand Tree, the answer "I can't remember" is accepted. Apology: sorry, I did the quest when it came out and only just saw your guide, so I am not 100% sure of the exact wording of the answer. How did I find this out? Well, I run with smart cursors turned on because, despite looking horrible, they are helpful. When I got the 'do something here' cursor, I straight away right clicked to search the picture without ever examining it. When the question comes up, I had no idea and hadn't seen it 'in-game' so had to actually tell the truth (shock! horror!).
