Harry recently applied for insurance and was surprised that his wife, who is the same age, was quoted lower premiums for the same coverage amount. Harry has a better credit rating than his wife and works as a construction worker, making $80,000 annually. His wife is a cashier at a local grocery store and makes $30,000 annually. Which of the following factors could have led to this? 

a) His age 

b) His gender 

c) His income level 

d) His credit rating