Four researchers are each conducting an experiment to test whether talking
to plants helps them grow faster. Each researcher puts 10 plants in a room,
where they are talked to every day, and 10 more in another room where they
are not talked to at all.
Select the researcher who is applying control variables correctly.
a.) Harvey makes sure that the plants in both rooms are planted in
the same soil.
b.) Alphonse feeds each set of plants a different kind of fertilizer.
Oc.) Mathilda varies the amount of water that each plant is given.
d.) Jackie decreases the light levels in one of the rooms to test if
that also has an effect on growth.