I dont understand my science work

Rank the three variables in terms of how strongly they affect the "species" composition of the bacterial communities. place the variable with the weakest effect on the left and the variable with the strongest effect on the right.

Where in the body can you find chemoreceptors? a. on the skin and ears, to detect pressure, touch, motion, and sound b. on the retina, to detect a single photon of light c. on the skin, to detect temperature or specific chemicals d. on the tongue and in the nose, to detect taste or odor

Why reason best illustrates why hershey and chase chose to use viruses in their experiment?