Ddt is a dangerous environmental pollutant because

DDT stands for Dichlorodiphenyl Trichloroethane.DDT was used in theas a pesticide Second World War to protect the troops and civilians from the spread of malaria and other diseases. Today DDT is used for insect control. 
But DDT harms the environment and the human health. 
There is an evidence that links DDT with severe declines in bald eagle populations due to thinning eggshells.
So, DDT is dangerous environmental pollutant because it is toxic.

The answer is a) carbon-12

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 .