Because the bottle suddenly falls onto the ground and breaks.
句意:兔子为什么哭?
根据第四段第2-5行:
"Bang!" The bottle suddenly falls onto the ground and breaks. Rabbit cries sadly, "Oh, my dreams!"
“砰!”瓶子突然掉到地上摔碎了。兔子伤心地叫道:“哦,我的梦!”
故答案为:Because the bottle suddenly falls onto the ground and breaks.