9.
Your Answer is
Correct Answer is C
Explanation
Option D: There are complete sentences before and after the underlined part. This option does not have a conjunction to connect two sentences, which is wrong.
Item A: When the leading adverbial clause is placed after the main clause and the main clause is not separated by a comma, and the logical relationship is wrong, the main clause is not an action that occurs at the same time.
Item B: Whom cannot be used for modifiers, wrong. Only in which means "through the mortise and tenon structure, one end of the board is embedded in the other end".