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.

we need more information in order to answer.

to eliminate ambiguous remote or broad reference it is necessary to focus on anaphoric reference. by definition "anaphoric reference means that a word in a text refers back to other ideas in the text for its meaning." the references should be clear and leave no room for ambiguity.

in the first case the pronoun it probably refers to the car but it has not been mentioned before so we should replace it for the car. in doing so the statement becomes clear.

in sentence number   two   the pronoun he refers to charles dickens the author. yet, the first half of the sentence is about the book a tale of two cities. to repair this it would be better to rephrase the first half : after i read   a tale of two cities by dickens, he so as to remove the remote reference.