Detailed Instructions: In this task, you're given a question, along with a context passage which has extra information available on certain terms mentioned in it. Your job is to determine which sentence(s) from the passage can be used to search for further information needed to answer the question.
Problem:Question: How many books has the author of the children's book that inspired the character of Princess Fiona written? Passage:Created by screenwriters Ted Elliott and Terry Rossio, Fiona is loosely based on the unsightly princess in William Steig's children's book Shrek!, from which her role and appearance were significantly modified. The screenwriters adapted the character into a princess under a shapeshifting enchantment, an idea that was initially greatly contested by other filmmakers. Fiona is voiced by actress Cameron Diaz. Comedian and actress Janeane Garofalo was originally cast as the character until she was fired from the first film with little explanation, although it is believed that the producers found Garofalo's sarcastic approach to the princess unsuitable after Shrek's original voice actor died. Fiona was one of the first human characters to have a lead role in a computer-animated film, thus the animators aspired to make her both beautiful and realistic in appearance. However, an early test screening resulted in children reacting negatively towards the character's uncanny realism, prompting the animators to re-design Fiona into a more stylized, cartoonish heroine.

Solution:
Created by screenwriters Ted Elliott and Terry Rossio, Fiona is loosely based on the unsightly princess in William Steig's children's book Shrek!, from which her role and appearance were significantly modified