Final answer:
Option (B), William Pitt the Elder was the key British leader who turned the tide of the war in favor of England by focusing on North America and supporting the military effort with extensive resources.
Step-by-step explanation:
The British government leader who turned the war in favor of the English during the critical period of the Seven Years' War was William Pitt the Elder. Pitt was instrumental in shifting the focus of the war to North America and provided substantial military resources which significantly aided the British war effort. In 1758 and 1759, the British, with the help of their colonial and native allies, were able to capture key French territories such as Quebec and Montreal, effectively leading to the collapse of the French empire in North America.