Final answer:
The rule for replacing 'us' with 'i' in plural form is based on understanding the subject and object distinction.
Step-by-step explanation:
The rule for replacing 'us' with 'i' in plural form is based on understanding the subject and object distinction. When 'us' is used as a subject, it should be replaced with 'we'. For example, 'We citizens must vote in order to make our voices heard.' When 'us' is used as an object, it should be replaced with 'us'. For example, 'Legislators need to hear from us citizens.'