Strange QOTD. Please explain if you can.

<p>I don't quite get today's QOTD.
Choice "A" just doesn't sound right.
Could anyone please explain?</p>

<p>Their explanation is pretty clear. </p>

<p>“Choice (A) is correct. It avoids the errors of the other options by correctly using the preposition “as” to introduce the “wide range of purposes” for which the gong is used.”</p>

<p>I’m not completely sure but i think
“purposes” … “as” is a type of idiom. since the only choices that contain as are A and E, let’s look at those. E would make the sentence a run on, which would make A the best choice.</p>

<p>I’m not sure if that made any sense. It’s really early and it’s a really odd sentence.</p>

<p>The purpose of the gong are not "a military signal, a rhythmic accompaniment for vocal performance, and a ritual instrument. The purpose of the gong is to be used as “a military signal, a rhythmic accompaniment for vocal performance, and a ritual instrument.” The key word here is “as.”</p>