单项选择题
Are responses to odors acquired as a function of the emotional context in which they are initially perceived Researchers recently conducted a study in which a novel odor was paired with either a positive or negative emotional experience. Ratings associated with the test odor varied in accordance with the paired emotion, such that the odor was perceived as either congenial or noisome, depending upon the quality of paired experience the participant had. Olfactory sensory attributes may produce an unlearned impact when odors are irritating; in these cases discomfort is experienced simultaneously to odor sensation, an event occurring when stimulation of the trigeminal nerve occurs coterminous with olfactory sensation. Many odors elicit trigeminal stimulation to varying degrees, so that the subjective distinction between pure odor and trigeminal irritation is not possible to make, though scientists have precipitously ventured to suggest methods. While these cases may help explain why one may be immediately repelled by a certain scent, they unfortunately do not allow most scientists to establish which smells trigger innate reactions.
The primary purpose of the passage is to________.（） A．point out that theories about the functioning of olfactory sensation have failed to change despite experimental inquiry
B．suggest means by which the impact of odors that irritate human subjects may eventually be lessened
C．describe the attempt of scientists to understand the degree to which odor perception is learned or innate
D．demonstrate that efforts to understand the psychobiological basis for human perception is too difficult for modern laboratory techniques
E．describe how the emotional pairing process in odor sensation can lead to the experience of irritation