为什么大熊猫以前是食肉动物,现在变成了素食动物?请用英文回答,在用中文翻译一下意思.

很久很久以前，地球经历了冰川导致的气候突变，大熊猫只残存在四川、甘肃等地区。那些地方生长着大量竹子，但却很难捕到活的猎物，大熊猫只有逐渐改变食性，才能生存下去。长期适应环境的结果，大熊猫从食肉变为食竹，它的臼齿也变得特别宽大，适于磨碎竹的纤维。

当然，大熊猫偶然也吃其他小动动，如见到了竹鼠，它就一巴掌将竹鼠打死，然后美餐一顿。

Long long ago,the Earth has experienced the climate sudden change which the glaciercauses,the panda only survives in area and so on Sichuan, Gansu.These places are growing the massive bamboos, but very is actuallydifficult to seize the live game, the panda only has the gradualchange feeding habits, can survive gets down.Adapts to circumstances or environment for a long time the result, thepanda becomes the food bamboo from the food meat, its molar alsochanges specially spaciously, is suitable for to grind the bamboo thetextile fiber.
Certainly, the panda accidentally also eats other slightly moves, ifsaw the bamboo rat, it kills on a palm of the hand the bamboo rat,then fine food.