Answer:
Correct answer is D. It lifted morale and gave the American forces a much-needed victory.
Explanation:
A is not correct as the war didn't ended until 1783.
B is not correct as he already was leading army in the battles of Boston and Long Island.
C is not correct as France entered the war after the battle of Saratoga.
D is correct as it lifted the morale of the army after the victories of Trenton and later Princeton.