How does a prosecutor choose what "cl of felony/misdemeanor"?

according to the crime, not evidence, because some people have no evidence they murdered but its still a felony. Also they might change it, i got arrest and got 3 felonys, when i went to court they said i had misdemeanors the racist cop just made it more severe than it was. Also it can depend on your age and everything, its a bit different for minors, but if the crime is severe enough they can go to adult court and tried as adults. Also a crime can be more severe if it has enhancements like 186.22 which is you did the crime for benefit of a street gang, or it was gang related