But (B) only targets the relationship between anchovies and plankton consumption without consideration of other factors that could taint the anchovies. (B) would be sufficient only if we assume that the consumption of plankton was the only factor that would cause anchovies to be tainted.

I think for question 13, if E said "would," then it would be a good candidate for the right answer. The fact that they phrased it "did not" plays into why it's wrong. "Did not" could include the likely possibility that they were simply never asked and never noticed code-switching, as J.Y. mentioned. "Would" would describe a hypothetical situation where they were asked, and if they didn't explain code-switching the same as they would've prior, then it would be more plausible that the researchers introduced bias. But also, the author's claim is code-switching isn't always explained by situational factors, and the example of the family is used to exemplify this claim. So, that's another reason why A is relevant and is the correct answer since it directly says that code-switching only occurred during situational shifts thus weakening the claim/interpretation that this code-switching happened at least in part due to rhetorical reasons.

You would check in, which is a quick process verifying your identity and lock up your phone, wallet, etc., then you'd likely start almost immediately. It won't be synchronized with everyone else in your time slot. I showed up early and I'd recommend that as well. Also, you'll be given scratch paper, a pencil, and access to noise blocking headphones, and the room is filled with a bunch of computers and probably other students also taking a proctored test. The default test is on the computer with the same format as the one online, and you would only get the test on paper if you request that as an accommodation. You'll be given a 10 minute break at the halfway point, where you can use the restroom and I think eat a snack with the proctor's permission (might have to check on this one). I took it in DC and it felt pretty relaxed overall to be honest. I like the benefit of not having to do a room scan, worrying about whether my internet was going to go out, proctors interrupting me, etc.