What part of the sentence creates ambiguity about who was on the way to school?

The phrase "on the way to school" creates ambiguity because it does not specify who is actually making the journey. This vagueness can lead to confusion about the subject of the action. Without additional context, it is unclear whether "he," "she," or another subject is on the way to school, leaving the reader uncertain about who is being referred to. The other options either provide specific subjects or actions that do not contribute to this ambiguity, focusing instead on different aspects of the sentence.