Sarah and evan are in the same science class. the teacher asks the class to design an experiment to determine the effect of acid rain on limestone. sarah designs an experiment which uses chalk and carbonic acid at a ph of 5.7, because she knows that chalk has the same chemical make-up as limestone and she knows that acid rain is primarily made up of carbonic acid at a ph around 5.7. evan designs an experiment which uses limestone tiles and acid rain collected from the environment. how do these experimental methods compare?