I just started doing these puzzles in dads New Scientist magazine and I finished them all in about 20 seconds each, whereas everybody else took at least a minute for each question. Now, this got me all hyped up about the possibility that I could be smart or something... apparently not, because this question is driving me insane. Please please help, because I am DYING here!

[] = box

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WHAT is the '??'
(I imagine this would work better if you were to draw it out or copy and paste it into a text document at it in your preferred browser)