"When would you use string as opposed to String?" or "Why do you think that the corelib int Convert.ToInt32(double value) method has this name and return type?"
These are more open; allow the candidate to explain that there's little practical difference between string and System.String; that it comes down to coding style; that there are aliases for int to System.Int32, which are probably VC++ showing through a bit (both the fixed size integer types and the underlying problem that made them necessary/useful); that it helps non-.NET consumers know what "int" means etc etc.
IMO it's still not a great interview question though (once you verify that the developer knows the basics) - I think that a lot of devs wouldn't know the ins and outs of this, simply because they'll hardly ever need to appreciate the difference (ie put it in your coding standards that they need to use one and they can forget that the other exists almost entirely).