The part of the eye responsible for fine-tuning the refraction of incoming light is the

lens
retina
optic nerve
cornea

The lens i guess... im not entirely sure thoug

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 .

The answer to the question is d