Iron is a strong and useful metal.
铁是一种结实又好用的金属。
But it has a weak point.
但它有一个弱点。
It reacts with water and air slowly.
它会和水、空气慢慢发生反应。
The surface turns brown and flaky.
表面就变出褐色的、一片片的东西。
That is rust.
这就是铁锈。
Rust can make iron weak and broken.
铁锈会让铁变脆、坏掉。
That is why we paint iron things.
所以我们才给铁的东西刷漆。
