Which of the Following Statements Are Correct? Who an 'Expert

Which of the following statements are correct? Who an 'expert' is, is based on qualifications and/or past experience. There is no statutory definition except in rare circumstances such as who can provide expert evidence as to insanity.

A) An expert witness must always have recognised qualifications
B) Expert witnesses are limited to only providing opinion evidence within their field of expertise or if asked to do so by a court
C) A judge may call his own expert evidence
D) In general who an 'expert' is, is statutorily defined