So I don't think the previous commenter got it right, and I think this question is in fact busted. But I'd also like to hear people's thoughts.

The original logical relationship, we can agree, is I + F -> U. (inviting and functional --> must be unobtrusive).

@ writes that

"If egos have produced buildings which are not functional for public use, that must mean that these same egos have produced not unobtrusive buildings."

But that's not true. Failing the sufficient doesn't gaurantee that the necessary also fails. If the sufficient fails, the logical relationship ceases to exist.

As I got from a powerscore forum, the key here is in the fact that "modern architects have violated this precept." This means that for them, the logical relationship in the first sentence doesn't hold: modern architects produce inviting, functional buildings that are nevertheless not unobstrusive, or I + F -> /U.

Here's where I think the question got it wrong. The correct answer, B, goes "not functional --> not unobtrusive," or /F --> /U. Like @, here, the sufficient is failed, so the logical relationship should cease to exist.

B would be the right answer if it was a CBT question, or if in the stimulus they told you that modern architects are producing functional buildings. But the quetsion is a MBT that relies on an invalid logical relationship.

Taking a few days off to prevent burnout is a very worthwhile investment.

You can also take a PT and see how poorly you do to remind you of how far you have to go :)