When two continental plates of similar densities collide,
A. they remain level since densities in both plates are equal.
B. they both push back down into the mantle
C. one plate rides over the other one and forms a trench
D. they buckle upward and form mountains

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .