Answer: C. Having found their seats, the members of the orchestra began to tune their instruments.
Explanation: a participle is a word formed from a verb and used as an adjective or a noun. It can be in present (ending in -ing) or in past (typically ending in -ed). From the given options, the rewritten sentence that begins with a participle is the corresponding to option C: Having found their seats, the members of the orchestra began to tune their instruments, where the participle phrase "having found their seats" acts like and adjective modifying the noun "members."