What Is a Doctor Most Likely Checking for If He

What is a doctor most likely checking for if he uses a test to determine if a man is having night-time erections? 

A)  If the conditions should be classified as a primary or secondary problem. 
B)  If the condition is more likely to have a physiological cause versus a psychological basis. 
C)  If the condition can be effectively treated with a drug like Viagra. 
D)  If the condition is situational or global.