Which statement is always true A all lithium atoms contain the same numbers of protons B All lithium atoms contain the same number of neutrons C All lithium atoms have the same mass D the sum of protons plus neutrons is the Sam in all lithium atoms

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 .