Passage：…Sculptures must, for example, be stable, which requires an understanding of the properties of mass, weight distribution, and stress. Paintings must have rigid stretchers so that the canvas will be taut, and the paint must not crack, deteriorate, or discolor. These are problems that must be overcome by the artist because they tend to intrude upon his or her conception of the work. For example, in the early Italian Renaissance, bronze statues of horses with a raised foreleg usually had a cannonball under that hoof. This was done because the cannonball was needed to support the weight of the leg. In other words, the demand of the laws of physics, not the sculptor’s aesthetic intentions, placed the ball there. That this device was a necessary structural compromise is clear from the fact that the cannonball disappeared when sculptors learned how to strengthen the internal structure of a statue with iron braces (iron being much stronger than bronze)…

　　According to paragraph 2, sculptors in the Italian Renaissance stopped using cannonballs in bronze statues of horses because

　　A. they began using a material that made the statues weigh less

　　B. they found a way to strengthen the statues internally

　　C. the aesthetic tastes of the public had changed over time

　　D. the cannonballs added too much weight to the statues

　　正确答案是B。