The sentence that includes an unclear pronoun is:
"Jamal and his cousin left at the same time, but she reached the park before he did."
In this sentence, "she" could refer to either Jamal or his cousin, making it unclear. To correct it, you could specify who "she" refers to by using their names. For example: "Jamal and his cousin left at the same time, but his cousin reached the park before he did."