In this task, you're given a passage, further information available on a particular linked term from the statement, and an answer term. Your job is to generate a question that can use the information provided to obtain the given answer. You should use the information on both passage and link information to create the question. Note that the answer to the question should be exactly the given answer, and if the answer is none, the answer to the question shouldn't be obtainable from the passage or linked information.

Passage: In 2009 it was announced that the feature film Testament of Youth was in development by BBC Films and Heyday Films producer David Heyman, and was to be directed by James Kent. This had the support of the Vera Brittain Estate, Brittain's daughter Shirley Williams, and Brittain's biographer Mark Bostridge who is acting as consultant. Saoirse Ronan was cast to play Brittain in 2012 but was replaced in December 2013 when it was announced that Alicia Vikander would play Vera Brittain in the film which was released in late 2014 as part of the First World War commemorations. On 4 February 2014 Kit Harington joined the cast to play the role of Brittain's fiance Roland Leighton. On 13 February 2014, Colin Morgan, Taron Egerton, and Alexandra Roach were announced to have joined the film's cast. An ensemble cast was later confirmed as filming began, including Dominic West, Emily Watson, Joanna Scanlan, Hayley Atwell, Jonathan Bailey and Anna Chancellor. It substituted Merton College, Oxford in the scenes showing Brittain's time as a student at Somerville College, arguing that filming in Somerville itself would been too difficult in light of the new buildings constructed there since the film's time period.
Link Information: none Answer: none
Why was Saoirse Ronan replaced by Alicia Vikander?