Punctuations are used in a sentence to organize and structure it properly. Moreover, it is used to create clarity and sense or to stress in a sentence. For example quotation marks " ", full stop (.), commas and so on.
Commas are frequently used punctuation in a sentence, hence they are used to create a short pause in a sentence.
In the above sentences, the sentence which is punctuated correctly is C. After they rested a few days, the aliens revived sufficiently to explore.
When starting with the dependent clause, the sentence is punctuated after the dependent clause. In the above sentence dependent clause is <em>“After they rested a few days”</em>, hence as compared to other sentences it is punctuated correctly.
The rime of the ancient Mariner is a ballad stanza and the rest are blank verse
If you want an explanation:
A blank verse doesn’t rhyme and a ballad does
