A.I. Explanation:

Option 1: "they began using a material that made the statues weigh less"

Explanation: This option is incorrect because the text does not mention a change in material that reduced the weight of the statues. Instead, it focuses on the internal strengthening of the statues with iron braces, which is a different concept.

Option 2: "they found a way to strengthen the statues internally"

Explanation: While the text does state that sculptors learned to strengthen the internal structure of statues with iron braces, this option does not address why they stopped using cannonballs. The reason is more about the cannonballs being unnecessary rather than the internal strengthening itself.

Option 3: "the aesthetic tastes of the public had changed over time"

Explanation: This option is incorrect as the text does not discuss changes in public aesthetic tastes. The focus is on the structural necessity of the cannonball and its eventual removal due to advancements in statue construction.

Option 4: "the cannonballs added too much weight to the statues"

Explanation: This option is correct because the text implies that the cannonball was a structural compromise due to the weight of the raised foreleg. Once sculptors learned to strengthen the statues internally, the cannonball was no longer needed, indicating that it was indeed adding unnecessary weight.