The missing semicolon " ; " in the option A is the reason why I chose option 'A'. However, after checking the original sentence, I am perfectly fine with option 'D' being the correct choice. [Edit] Just realized that 'A' is laden with errors. Corrected those errors in the end.
Small business owners play important roles in a community, providing products from local manufacturers, independent craftsman as well as international artists; they hire both older and younger workers; and occasionally bring new life to dilapidated shopping centers.
A) they hire both older and younger workers and occasionally bring
D) hiring both older and younger workers; and occasionally bringing
My two cents -- Many of you said that 'they' doesn't have a proper antecedent.
If, there is no semicolon in the given sentence as stated in option A, then we have two independent clauses connected by a semicolon. So, "they" can still refer to subject of the first clause (as both these clauses, though independent, are still connected by closely related idea)
I will correct the sentence, in which case 'A' can be the answer. Note the highlighted words.
Small business owners play important roles in a community, providing products from local manufacturers,
and independent craftsman as well as international artists; they hire both older and younger workers occasionally
bringing new life to dilapidated shopping centers.
Clauses separated by a ";" should be parallel and should also be closely related.
Nevertheless 'D' is the correct option--> nicely disguised parallelism.