Hi pairakesh10,
Thank you for your question. Let's tackle this question one problem at a time. After looking over the possible answers, a few differences jumped out that we can address:
1. serve vs. serves
2. ending with semicolons vs. commas
3. comma placement in the rest of the answer
Let's start with #1: serve vs. serves. Since the verb is referring to the singular "a unique system," the verb needs to be the singular "serves." Therefore, let's rule out answers B & C because they use the plural "serve."
Next, let's look at #2 on the list: ending with a semicolon vs. a comma. We need to make sure whatever comes after the word "relaxed" is punctuated properly. If it's an independent clause, it needs a semicolon. If it's a dependent clause, it needs a comma or no punctuation. Let's see if they work:
a) legs, serving as a kind of sling in which, with their body weight suspended and the muscles in their limbs completely relaxed,
the result is they are able to sleep standing up.This is an independent clause, which means it could stand alone as its own sentence. Independent clauses need to be separated by semicolons - a comma isn't good enough and will create a comma splice. Therefore, this answer is
INCORRECT because of faulty punctuation.
d) legs that serves as a kind of sling in which,
with their body weight suspended and the muscles in their limbs completely relaxed, having the result that they are able to sleep standing up.
This answer is
INCORRECT because it doesn't make sense how it's punctuated. By putting the phrase I crossed out above between commas, it is now a non-essential phrase. If we take it out, the rest of the sentence doesn't make sense. Therefore, the commas are in the wrong places for this to work, making it wrong.
e) legs that serves as a kind of sling in which their body weight is suspended while the muscles in their limbs are completely relaxed
; as a result, they are able to sleep standing up.This is the
CORRECT answer because it uses a semicolon after "relaxed" to show that everything after it is part of an independent clause.
After looking at subject-verb agreement and punctuation, it's clear that
E is the CORRECT answer!