In an atom, the nucleus contains an equal number of protons and electrons all the protons and neutrons all the protons and electrons only neutrons only protons

The protons and the neutrons

Ithink it’s 3 as the answer.

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 .