What do these substances have in common? apple juice helium gas salt water copper wire

Iwould you figure it out but you don't have a picture or in your question as to what the physical property you're looking for is

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 .