Many People Were Surprised by the Results of the 'Brexit

Many people were surprised by the results of the 'Brexit' referendum because the 'remain' outcome was the favoured in many polls preceding the vote. Which of the following research methodology flaws may have led to this inaccurate prediction?

A) The estimates may have been based on data from a sample that was not representative of the population
B) The wording of the questionnaire items may have been vague and biased
C) Self-presenting bias may have prevented respondents from voicing their honest opinions
D) All of the above