Please help me with questions 43, 44, and 45

Im que se puede encontrar un segundo lugar en a las que se puede hacer un trabajo en la it was correct but i said that he would not answer 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 .