Question

In an experiment to study the effect of ultraviolet light on bacteria, it was concluded that ultraviolet light has a sterilizing effect on bacteria. Which of these observations could have led to this conclusion?

Answer 1

Sterilizing of bacteria; they do not grow as much and die off? 

Ultraviolet light stopped the replication process of bacteria. 
Stopped or slowed this process, hint the sterilization.  

The question doesn't directly ask this but, after a while a lot of bacteria become immune to treatment especially antibiotics.