If so, then your preparation for this question was apparently inadequate, and you really did not know the material.
[Solution: More effective use of study time.]
If so, then you may have been unfamiliar with the terminology used in the choices of answers.
[Solution: More effective use of study time.]
If so, you may have misread the question -- one missed word can completely change the meaning of a sentence. Most of the Sample Questions have several variations; a quick glance at the question may be insufficient to determine the correct answer. Another possibility is that you may have failed to read and carefully consider each answer; sometimes an answer may sound good, but there is actually a better choice to be made.
[Solution: More careful reading of exams.]