What Has Canadian Research Shown to Be One of the Simplest

What has Canadian research shown to be one of the simplest and most effective things a parent can do to enrich a child's environment?

A) encourage children to read on their own rather than reading to them
B) keep mirrors out of sight so that children don't become obsessed with themselves
C) read to two- and three-year-olds several times a day
D) keep the environment consistent by not rearranging their room through their childhood