Which one is it I am confused A, B,C or D

What factors contribute to the effect an environmental toxin has on the human body?

Prior knowledge can be gained from personal experience and a) forming well-developed hypotheses. b) listening to opinions of other people on a topic. c) researching previous experiments and results on a topic. eliminate d) no other methods. it can only be gained by personal experience.

The hershey and chase experiments involved the preparation of two different types of radioactively labeled phage. which of the following best explains why two preparations were required? a. the bacteriophage used in the experiments was a t2 phage. b. it was necessary that each of the two phage components, dna and protein, be identifiable upon recovery at the end of the experiment. c. each scientist had his own method for labeling phage, so each conducted the same experiment using a different isotope. d. establishing the identity of the genetic material required observation of two phage generations.