Which of the following contains a vague pronoun reference?

 - Zach and his best friend go to the same college, but he is graduating this coming June.
 - Zach and his best friend go to the same college, but Zach is graduating this coming June.
The first answer choice contains a vague pronoun reference. The pronoun he could refer to Zach or his best friend.
The second answer choice shows a possible correction for the vague pronoun reference. He has been replaced with Zach.
Zach and his best friend go to the same college, but Zach is graduating this coming June.