Final answer:
Poor blood circulation is not a common cause of surface stains on nails.
Step-by-step explanation:
The correct answer is d. poor blood circulation. While nail polish, food dyes, and smoking can all cause surface stains on nails, poor blood circulation is not a common cause. Nail polish and food dyes can leave stains on nails due to their pigments, while smoking can cause yellow stains on the nails due to the nicotine and tar present in cigarettes.