Just like a substitute teaches your class,/when she's asked to fill in for your teacher,/a pronoun steps in as a sub for a noun,/ becoming the star of the feature.
Gobi bears may just be the most unusual bears on the planet: they're the only bears that live in a desert, they eat mainly plants, and they're extremely rare.
When an injured fox (crippled by a steel-jawed trap) hobbled into Cherie Masons yard one morning, it was the start of a special and unusual relationship.