Which of the following contains a vague pronoun reference?
A. When Molly was researching the lives of famous scientists, one source said that Albert Einstein had a speech impediment when he was a child.
B. When Molly was researching the lives of famous scientists, it said that Albert Einstein had a speech impediment when he was a child.
Identify the correct option from the choices provided and respond with the letter of the correct option.
Answer: B