Meaning Analysis- There is a pact between two warring parties. Based on this pact one of the parties agreed to return the occupied city to the other party. The former party returned the occupied city after six months.
Error Analysis- The subject and the verb make sense and agree in number. The simple past tense has been correctly used to present facts. The usage of the pronoun "it"makes sense and leads to no ambiguity. The usage of semi colon separates two independent clauses. There is no error in the Original sentence.
Correct Answer- Choice A
Choice A- Correct per the above analysis
Choice B- This choice is incorrect and is too wordy. The usage of past perfect tense had passed is incorrect as there is no related event to show sequencing of two past event.
Choice C- This choices changes the meaning of the sentence. Per this choice the party returned before six months. Per the original sentence the city was returned after six months. Also, this choice makes the sentence wordy.
Choice D- Idiom error. The usage of more is incorrect. The correct usage should be six months later.
Choice E- Idiom error leading to meaning error. The usage of a soon as is incorrect. The correct idiom is as soon as. Also, this choice repeats the same error in Choice C and D.