27.

Answer and Explanation

Your Answer is

Correct Answer is A

Explanation

yet is an adverb here, used as a parenthesis. Therefore, separate the sentence stem with a double comma, and A is correct.

Item B/C: Whether leading clause, there can be no symbols between it and the following clauses.

Item D: yet is used as a conjunction, and the two sets of subjects and predicates cannot have two conjunctions.