Answer: The sentence that is complete and properly punctuated is D. From 10% to 20% of school-aged children develop intense anxiety over some issue; for instance, children with school phobia feel intense apprehension about attending school.
Explanation: Sentence D. is the only one that is complete and properly punctuated because it expresses a full idea and makes a good use of punctuation marks. Punctuation rules state that, when using "for instance" in a sentence, a semicolon must precede this term and a comma must come after it. In that way, as D. is the only option that includes a semicolon before "for instance" and a comma after it, this sentence can be considered properly punctuated.
