Which of the following statements is NOT true about "presumptions" in criminal law?
a. Presumptions in criminal law cannot be challenged by the accused.
b. Some presumptions assist the Crown in establishing facts in issue, which may be critical to the success of a prosecution.
c. Some presumptions create a reverse onus in which the accused may be required to disprove or challenge a fact.
d. Presumptions may be used to establish the mens rea in some criminal trials.