Simplify the following text for a Grade 9 native English-speaking person.
Original: Since Whedon was directing Serenity at the time and required time to research Wonder Woman 's background , he did not begin the screenplay until late 2005 .
Simplified: Because Whedon was directing Serenity at the time , and needed time to learn Wonder Woman 's background , he did not start writing until late 2005 .