The correct punctuation for the sentence should be:
B. documents; that
Explanation:
1. In the sentence, "Identity documents (IDS) are documents that are used to prove a person's identity," the correct punctuation is a semicolon (;) followed by the conjunction "that." This punctuation is used to connect two closely related independent clauses or phrases.
2. Option B correctly places the semicolon before "that," maintaining the logical connection between the two parts of the sentence.
Therefore, option B - "documents; that" - is the correct punctuation choice for the sentence provided.