Lilly's 12-year-old son used to get out of bed easily and early on school days, but lately he has been hard to wake. While reading a parenting book, Lilly came across the theory of "delayed phase of preference," in which sleep patterns shift when young people start to go through puberty. In this example, a theory helped Lilly .
Select one:
A. generate a discovery
B. change her own behavior
C. gain practical guidance
D. design an experiment