The flocks of geese flew through the air for miles until they were tired and had to land to rest. No mistake There must be a noun or pronoun in the sentence that can act as a precursor. The pronouns it, this, that and that can lead to a vague reference pronos if they refer to something that was previously mentioned in another sentence: pronouns play an important role in the English language. Pronouns replace nouns, so your writing could repeat itself without pronouns. Here are some common mistakes to watch out for in pronouns. For people living in extremely cold climates, putting on warm mittens and boots just to cross the street is a necessary precaution to protect themselves from the cold. No errors. The tree-toothed spider migrates from the Amazon to the north, where it was previously at home. No errors.