"Why Do We Do Natural Experiments?" Asks a Student

"Why do we do natural experiments?" asks a student. "After all, each disaster that causes a natural experiment is unique." A good answer would be:

A) "They are an inexpensive ways to gather detailed individualized data on disaster survivors."
B) "They provide the highest levels of internal and external validity when studying the effects of disasters."
C) "The sheer volume has allowed researchers to identify patterns of reactions in those persons involved in disasters."
D) "The findings to date have been instrumental in helping prevent casualties from natural disasters."