<p>The intricate (pattern on) a butterfly's wing (is composed of thousands) of microscopic scales, each (of which) (is) the product of a single cell.</p>
<p>the correct answer was E, no error</p>
<p>the problem i have with this is the idiomatic phrase "pattern on." why can it not be 'pattern of'?</p>
<p>the point of these types of identify-the-error questions is not to find the way you would say it but to find anything wrong grammatically with the sentence. your suggestion to change the sentence certainly would make some sense as well, but the original phrase ‘pattern on’ isn’t grammatically incorrect. in fact, it’s even more appropriate. you wouldn’t say “look at that pattern of the wall”. you can’t choose something as a wrong answer just because something sounds a little better. the wrong answer has to be WRONG.</p>