1) the halftime performers whirled through a complex series of choreographed moves. 2) twirling their batons so fast they resembled helicopter blades.
which option explains why section 2 is a sentence fragment?

a. it begins with participle verb form and therefore must be linked with what it modifies in an independent clause or main sentence.
b. it does not contain a noun.
c. it begins with a coordinating conjunction and therefore must be linked with an independent clause or main sentence.
d. it does not contain a verb.