Murray appeared in court as a witness for his friend Maureen who was charged with driving while intoxicated. Murray testified that Maureen was not the driver of the vehicle when in fact he knew that she was. Despite Murray's testimony, Maureen friend was convicted. Given these facts, which of the following statements is true?
a. Murray has committed perjury.
b. Murray cannot be charged with perjury because his testimony was not material to the case.
c. Murray cannot be charged with perjury because he was entitled to use immunity under the Federal Constitution.
d. Murray cannot be charged with any offense because, despite his false testimony, his friend was found guilty.