When answering this type of question, it is important to focus primarily on providing an answer to both options in the question, as well as providing a clear judgement. This means providing an explanation for how significant the British policies and French entry into the war were in bringing about the victory of the American colonies. The judgement is reached via the conclusion, in which you would say which factor was more significant and why. As this is only a 10m question an introduction is not needed. However due to the short nature of the question structure is key. Hence your answer will follow a Point, Evidence, Explain and Link formula. I would try to write two full points for each side. For example- France began their active support of the war in 1778, through economic and military support. From this you would then go on to outline and explain each point. For example- France provided naval support in the form of a blockade as a result of the Franco-American treaty. This was significant as it had a direct impact on the colonial victory at the Siege of Yorktown in 1781, in which the naval blockade prevented supplies reaching the British troops on land, ultimately resulting in their surrender. Consequently, the French entry into the war was instrumental in the colonial victory due to the military support they provided. Then you would proceed to argue the other point (British policy) using the same formula. Finally, you would need to end with a conclusion which makes a clear judgment on which factor had greater significance and why.