（不定式作表语）我的工作是教他们英语。

My job is to teach them English.

把一根断成数截的铁棍连接起来的一个方法就是把铁加热至软化，然后用铁锤去锻打。句中heating和pounding均为表语。

One way to fit the pieces of a broken iron bar together is heating the iron until it softens and pounding it with a hammer.