To determine which conclusion the image best supports, we would need to analyze the content of the image. However, based on historical context surrounding France's involvement in the American Revolutionary War, it is well-documented that:
- France formed an official alliance with America during the war in 1778, making this statement true.
- Washington did indeed appreciate the support from France, particularly after the victory at Saratoga, but it is more accurate to say that the victory itself helped encourage France to formally support the American cause rather than giving credit directly to them for the victory.
- French soldiers and officers did not primarily act as mercenaries but rather as allies in support of the American Revolution.
- General Washington, as the commander of the Continental Army, did have authority to engage with foreign powers, although formal treaties would typically involve Congress.
Given the options and the historical context, the conclusion best supported would be:
France formed an official alliance with America during the war.