The best answer is D. According to the passage, the electrorecepors in the snouts of spiny anteaters responds to extremely weak electrical fields. The author of the passage contrasts these electroreceptors with tactile receptors, stating that it takes field strengths “about 1,000 times greater than those known to excite electroreceptors” to excite the tactile receptors on an anteater’s snout. The passage does not contrast the two types of receptors with regard to the characteristics mentioned in choices A, B and C.