The best response that explains why Pitt was key to Britain's victory in the French and Indian War is:
He paid more people to join the British forces and fight.
William Pitt, who was appointed as the Secretary of State, significantly increased British military spending and orchestrated the hiring of more soldiers and support for colonial militias, which was crucial in turning the tide of the war in favor of Britain. Through his strategies, he was able to mobilize resources and support that played a major role in achieving victory against the French.