Which of the following could have caused curve B to be different from curve A?
A. A bright light could have been present in reaction B.
B. More reactants could have been added to reaction B.
C. An enzyme could have been added to reaction B.
D. The temperature might have increased in reaction B.

D. The temperature might have increased in reaction B

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 .