How does a salt bridge improve a battery? O A. It keeps the electrolyte solutions neutral.
O B. It makes the redox reaction spontaneous.
O C. It blocks the flow of ions between the electrolytes.
D. It causes the metals to oxidize faster.

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 .