Dry ice (solid carbon dioxide) can be used to lower air temperature as it transforms into a gas without melting into a liquid. This process is a practical use of what?

You know how the first one if filled up like the objects do the same but with the other categories

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 .