Final answer:
Incongruency can lead to cognitive dissonance, causing psychological discomfort. People may become defensive and engage in denial, distortion, or reaction formation to protect their self-esteem and maintain a consistent self-image.
Step-by-step explanation:
In psychology, incongruency can cause people to get defensive due to cognitive dissonance, which is the psychological discomfort arising from holding two or more inconsistent attitudes, behaviors, or cognitions. This discomfort often prompts defense mechanisms such as denial, where an individual refuses to accept reality because it is too threatening; distortion, which includes rationalization to justify or explain away the discomfort; and reaction formation, in which someone might express the opposite of their actual feelings to reduce their anxiety. Therefore, the answer to the student's question is: incongruency causes people to get defensive primarily through the mechanism of denial (C).