Final answer:
The British army lost the Revolutionary War due to a lack of morale among their soldiers.
Step-by-step explanation:
The answer to your question is A) lack of morale among their soldiers. Despite having a well-trained and experienced army, the British suffered from low morale among their soldiers during the Revolutionary War. The soldiers were far from home, faced harsh conditions, and lacked the motivation to fight for a cause that they did not fully support. This lack of morale weakened the British army and ultimately contributed to their defeat.