How Have Classification Systems for Living Things Changed Over the Years

How have classification systems for living things changed over the years?

A) Scientists have always recognized five kingdoms of living things, but the placement of species within those kingdoms has changed.
B) Until the last 20 years, organisms had been classified first as animal or plant. Recently, a five-kingdom system became the preferred classification system.
C) The three-domain system has been introduced within the last 30 years, to supplement the five-kingdom system.
D) The exact organization proposed in the eighteenth century by Carl Linnaeus has recently been reinstituted by scientists.