What should replace the underlined pronoun to correct the pronoun shift error? he I they us

Read the sentence. marissa heard the class bell ringing loudly walking down the hall. what is the best way to revise this sentence? `marissa heard the hall ringing loudly walking down by the class bell. `marissa heard the class bell walking down the hall ringing loudly. `walking down the hall, marissa heard the class bell ringing loudly. `walking down the hall, the class bell ringing loudly marissa heard.