Which of the following materials is likely to be the best insulator?
-silver
-phosphorus
-silicon
-calcium

The element most likely to be the best insulator is the worst conductor among the four when you test for their conductivity. The answer among the four options given is 'phosphorus'. I hope this helps you on your assignment. 

What? i don’t understand

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 .