The correct answer is B. Having found their seats, the members of the orchestra began to tune their instruments.
Step-by-step explanation:
In grammar, a participle refers to a word that has been formed by adding -ing, -ed or -d to a verb and that acts mainly as a modifier (adjective, adverb) rather than as a verb, this means participles modify another noun or even a verb in the sentence. Considering this, the sentence that begins with a participle and still includes the information of the original sentence is "Having found their seats, the members of the orchestra began to tune their instruments", because in this case the first word "Having" ends in -ing which is one of the main features of participles but besides this,the clause "Having found their seats" serves a modifier as it describes "the members of the orchestra" and therefore "having" is not a verb but a modifier and therefore, in this case, it is a participle.