Which of the following contains a vague pronoun reference?

 - When Eva returned to the apartment that evening, she greeted Mary with a hug.
 - Eva greeted Mary with a hug when she returned to the apartment that evening.
The second answer choice contains a vague pronoun reference. The pronoun she could refer to Eva or Mary.
Eva greeted Mary with a hug when she returned to the apartment that evening.
The first answer choice shows a possible correction for the vague pronoun reference. The text has been rewritten so that the meaning is clear.
When Eva returned to the apartment that evening, she greeted Mary with a hug.