13.
Your Answer is
Correct Answer is B
Explanation
Item B: steady "stable" and rhythmic "rhythmic" are adjectives of the same level, and a comma is added in between, so B is correct.
A/C items: Adjectives modify nouns, multiple adjectives modify nouns, the last adjective and nouns are not separated by commas, so A/C is excluded.
Item D: There must be sentences before and after the semicolon, so D is excluded.