Hello,
The correct objective summary of the passage above is B.
The benefit of group work that is demonstrated in this example is enabling a complex task be broken down to simpler and fewer works. Since each individual had been given fewer task, it leads to increase of productivity while saving the time consumed in finishing the project.
Its A)
<span>It cannot be a independent clause because that phrase itself cannot be its own sentence. For example in the sentence "I need some water to drink.", "I need some water" is an independent clause, because it can be a sentence that makes sense not like "to drink", because that makes no sense. So as I said before I got to talking about clauses</span>