Answer: B- An ex-high school standout, he enjoyed a stellar college career at the University of Kansas.
An hyphen is a punctuation mark, that is used to join two related words or to break a single word into parts or placed between words which have different meaning. The use of hyphen is called as hyphenation. Here, the hyphen should be present in between ex-high school, which is describing a relation of person with the high school, means that the person was previous scholar of the high school.