Which of the following contains a vague pronoun reference?

 - After Anna separated the walnuts from the shells, she placed them in a wooden bowl.
 - Anna placed the walnuts in a wooden bowl after she separated them from the shells.
The first answer choice contains a vague pronoun reference. The pronoun them could refer to the walnuts or the shells.
After Anna separated the walnuts from the shells, she placed them in a wooden bowl.
The second answer choice shows a possible correction for the vague pronoun reference. The text has been rewritten so that the meaning is clear.
Anna placed the walnuts in a wooden bowl after she separated them from the shells.