牦牛

例句：

1. 1. The yak is a unique animal that is native to Tibet.
   牦牛是一种独特的动物，原产于西藏。
2. 2. The yak is an important source of protein for the local people.
   牦牛是当地人蛋白质的重要来源。
3. 3. The yak is known for its ability to survive in harsh mountainous environments.
   牦牛因其能在恶劣的山区环境中生存而闻名。