Why Might Someone Have Levels of Both Methamphetamine and Amphetamine

Why might someone have levels of both methamphetamine and amphetamine in his body?

A) The methyl chemical group breaks off of the amphetamine molecule if the freebase form of methamphetamine is smoked.
B) He took methamphetamine and some of the molecules were biotransformed into amphetamine.
C) The similarity between both compounds causes analytical tests to report both substances, when in fact, only of the compounds was administered.
D) Chewing lime improves oral absorption of methamphetamine in the mouth but also converts some of the molecules to amphetamine.