I'm reading the following paragraph and puzzled by "substituted for other tenses." What does it mean in relation to the particular example in quotation marks?
As a workaround, some writers have begun using the plural pronoun their as a singular, gender-neutral pronoun. For example: "Every student must turn in their homework." However, this approach becomes problematic when the plural pronoun they is used in the singular form and substituted for other tenses, which results in faulty syntax such as: “Tell that worker they must be careful on the roof.”