A conundrum solved.

I'm contracting for a big firm at the moment, and I've just started there, so have had to do some training courses. I don't mean actually learning to do my job — though I am having to do that, too, yes — but the corporate stuff that everyone has to do, regarding fire escapes and secrecy and so on. They're those online courses with multiple-choice tests at the end.

So one of them's about security and confidentiality and maintaining frankly paranoid levels of suspicion, and, in amongst all the easy stuff ("An evil spy asks for your Windows password. Should you (a) tell him, (b) not tell him, or (c) give him all the company's money?") was a genuinely tricky one. It went something like this.

You've been given a promotion and so will from now on have lots of highly confidential documents. You have therefore been given a filing cabinet. You put the documents in the filing cabinet and lock it. But where do you put the key?

Now, since the course has been at pains to point out how easy it is to drop your keys or to have them knicked, this is actually rather a difficult question. You can't put them in your pocket, 'cause of pickpockets. So you can't take them home with you. But neither can you leave them lying around anywhere at work, which would be the equivalent of not locking the filing cabinet in the first place. So what the hell do you do with them? I don't mind telling you, if it hadn't been multiple-choice, I'd never have figured it out.

The correct answer is: In a lockable key cabinet.

But of course.