by Sage Pearce-Higgins Mon Jul 17, 2017 6:58 am
Good job for taking a detailed look at this question.
The construction 'comma and' doesn't always mean that there are two independent clauses. It can also mean a list (and therefore a parallel construction). Take, for example, 'Jim eats chocolate, fruit, and bread.' No extra independent clause here. I know what you're about to say: in answer B above we have just two elements in the list. If the elements are longer, then we can add in a comma for clarity. For example: 'Jim eats chocolate made from the most expensive cacao seeds, and bread.' We have only two things that Jim eats, but the comma provides clarity.
In any case, as you analyze the sentence, the second independent clause doesn't make sense: 'Sources of building material and firewood, are providers of Employment for millions worldwide'. There's an unnecessary comma here, and it's a bit odd to say that the sources provide employment.