The correct answer D) it takes teamwork to get things done.
The theme that it is developed in this excerpt is it takes teamwork to get things done.
Former vice president Al Gore is using a quote to support his idea of teamwork. Gore invites people in his speech to abandon the conceit that working alone, isolated could be the answer to resolve important things such as climate change. He suggests that collective action and global mobilization are the correct answers to take action.