I believe the answer is:
a. it helped them work together during the hunt
d. it allowed them to develop future hunting plans
Prior to the development of spoken language, humans communicate through gesture. This allow other humans to have a general perception on what the communicator meant.
But through spoken language, the humans could understand each other's intend to the smallest detail. This make them able to create a detailed plan before hunting and communicate better at the hunting field especially if they cannot see each other's position.