Please Use the Following Information to Answer the Question(s) Below

Please use the following information to answer the question(s) below.
The contamination of soils with heavy metals has become more common as a result of the burning of fossil fuels, industrial activities, and agricultural fertilizer application. These heavy metals can be toxic depending on the concentrations that accumulate in an organism. A scientist hypothesizes that biological magnification of heavy metals in fragment-dwelling, insect-eating birds should be greater in forest fragments with relatively more edge habitat because edge-dwelling bird species may forage for insects in contaminated areas outside of the forest. Forest fragments with more interior habitat would not have as much biological magnification because insect-eating interior bird species would have less exposure to insects that contain heavy metals.
-The scientist finds that the heavy metal concentration in the insect-eating birds of a fragment does not depend on the relative amount of edge habitat of that fragment. Which of the following describes how experimental error may have influenced the results?

A) The density of birds is higher in edge habitat compared to interior habitat.
B) The forest fragments studied were too small, and there was no true interior habitat for birds to live in.
C) The insects eaten by both edge and interior birds do not differ in heavy metal concentration.
D) Heavy metals deposited from atmospheric pollution are equal across the landscape.