大多数四足动物，包括人类，都有两条前肢和两条后肢。

Most ___tetrapods, including humans, have two forelimbs and two hindlimbs.

沿海堤坝上放置了许多四脚混凝土块来抵御海浪侵蚀。

Many ___tetrapods were placed along the seawall to break waves and prevent erosion.