Which sentence is punctuated correctly?

a) the aliens suffered from exhaustion, after traveling several light years.
b) they needed some relaxation, when they finally landed their spaceship.
c) after they rested a few days, the aliens revived sufficiently to explore.
d) they needed all their energy, once they started hiking through terrain.

The question is asking us to say which sentence is punctuated correctly among the following sentences. For this, we can us the SOV rule: if something interrupts the Subject-Verb-Object -(other) order in a sentence, is should be separated by commas. here, it's option C: C) After they rested a few days (adverbial phrase), the aliens (S) revived (V) sufficiently to explore. So there must be a comma after "days" , but such a comma is not necessary in other cases. A) The aliens suffered from exhaustion, after traveling several light years. B) They needed some relaxation, when they finally landed their spaceship. C) After they rested a few days, the aliens revived sufficiently to explore. D) They needed all their energy, once they started hiking through terrain."

Refute it, showing why it is mistaken—an apparent but not real problem; acknowledge its validity or plausibility, but suggest why on balance it's relatively less important or less likely than what you propose, and thus doesn't overturn it; concede its force and complicate your idea accordingly—restate your thesis in a more exact, qualified, or nuanced way that takes account of the objection, or start a new section in which you consider your topic in light of it. this will work if the counterargument concerns only an aspect of your argument; if it undermines your whole case, you need a new thesis.