20.
Your Answer is
Correct Answer is H
Explanation
one of ... is an apposition, for the explanation of principal dancer, so it needs to be separated by symbols. A dash here indicates emphasis.
Item F: There is no sentence after the period, wrong.
Item G: The semicolon is not a sentence, wrong.
Item J: The apposition here requires a comma or a dash, so the position of principal dancer is very clear, and the subsequent modifications are not limited.