The best answer is C. In the experiment described in the first passage, researchers described the electroreceptors in the anteater’s snout as “clustered” at the tip. Thus, it can be inferred that nervous activity was not recorded across the entire snout, but only in certain areas. Therefore, some areas of the snout, including those containing the tactile receptors, were not stimulated by the weak fields used in the experiment, as choice C suggests.
There is no information in the description of the experiment provided in the passage to suggest A, B or D.