According to Wagner, "decision$-$making capacity" or "competency" refers to what?

a$.$ The capacity to make good decisions.

b$.$ The capacity to understand and explain the options and their implications, and to give a rational reason would decide on a particular option instead of others.

c$.$ The capacity to self$-$diagnose and self$-$treat illnesses.

d$.$ The capacity to understand the options, but not their consequences or implications.