In Regard to Giving Credit to Contributors to Research Projects

In regard to giving credit to contributors to research projects in published reports,

A) a footnote is sufficient.
B) every person who contributed must be listed as a co-author.
C) the major professor of a dissertation study must be listed as first author.
D) appropriate credit must be given, but there are no firm rules.
E) individuals who were paid to assist do not have to be given any credit.