Concept:"Arrogant" means proud, thinking oneself better or more important than others. The opposite quality is being "modest" (humble, not boastful).
Solution:The storekeeper lost his customers because of his proud, superior manner.
The word opposite in meaning is "modest": a modest storekeeper would be humble with his customers.
A. "respectful" means showing respect to others; it is close, but it is the opposite of rude, not of proud.
B. "obedient" means doing what one is told; it is the opposite of disobedient.
D. "sympathetic" means sharing others' feelings; it is the opposite of unkind or uncaring.
Key point: The direct antonym pair is arrogant / modest (or humble).
Answer:Option C (modest)