Because it has no scientific explanation. As a matter of fact it has no explanation.
The things that black cats cause bad luck are a myth, and do not have any proof or explanation, meaning it cannot be concluded neither as a hypothesis nor scientific.
Hope it helped,
BioTeacher101
 
        
             
        
        
        
Answer: Alveoli 
Explanation: Alveoli of lungs are surrounded by extensive blood capillaries. The partial pressure of oxygen in the alveoli is higher than the blood entering the pulmonary capillaries, hence oxygen moves into the blood. Carbon dioxide in the lungs simultaneously diffuse out of the blood into the alveolar space.
 
        
             
        
        
        
Answer:
Personality. 
Explanation:
The mental disorders affects the thinking ability of the individual. The mental disorder individual shows abnormal behavior in the society and might feel anxiety or feel awkward among the people.
The personality disorder is a type of the mental disorder in which the individual have unhealthy thinking level. This disorder affects the social status and his personality in the society. The occupational functioning become improper and requires the proper medical treatment.
Thus, the answer is personality.