Final answer:
The best meaning of 'I need you all on board' is 'I need you all to work with me.' It implies a sense of collaboration and teamwork.
Step-by-step explanation:
The best meaning of the phrase 'I need you all on board' is option D - 'I need you all to work with me.' This phrase is often used to indicate that everyone's cooperation and participation are required to achieve a goal or complete a task. It implies a sense of collaboration and teamwork.
It is essential to use inclusive language that suggests collaboration and a sense of teamwork. Phrases like 'I worry that,' or 'Do you also feel that...' can help foster an atmosphere of togetherness and shared responsibility, which is vital in collaborative group activities.