Why Is the Public Often Skeptical of Testimony from Expert

Why is the public often skeptical of testimony from expert witnesses?

A) Expert witnesses are biased and want their testimony in court to be consistent with what they have concluded in research they have published.
B) Expert witnesses generally are concerned about being sued if they give testimony that frees a person who goes on to commit a violent crime.
C) The public suspects that the side paying the expert witness determines the expert's opinion.
D) The public often does not fully understand the scope and breadth of expertise within academic fields.