Julian designs an experiment to see how well different liquids lubricate wooden surfaces. he sets up a number of identical wooden ramps and prepares to slide identical wooden blocks down them. he will time how long it takes each block to reach the end of the ramp. he covers one ramp with water, the second with motor oil, and the third with corn syrup.

what can julian use as a control group for the experiment?

a.
a block that drops straight down instead of sliding down a ramp
b.
a ramp with no liquid on it
c.
a second set of ramps covered with water, oil, and syrup respectively
d.
a ramp with no friction on its surface
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